Freight Delivery Truck Respawn
Each industrial building gets its own truck to deliver freight. The truck will locate nearby available orders and attempt delivery. Delivery may involve multiple buildings. All the freight on the truck must be delivered before the return trip starts.
If the truck returns from delivery quickly, it will spawn once per hour - each industrial building has its own timer. This way you get 24 truck deliveries per day.
If the truck is delayed, does not return in one hour (before the next truck would spawn... then the next truck doesn't spawn. The building resets the clock for another hour. This can happen when the gets stuck in traffic, or its freight shipment is far away. In this case, you get less than 24 truck deliveries per day.
For example: if a truck takes 2.5 hours to return, the next truck will spawn in 0.5 hour. The building keeps the timer. If this happens consistently to the same building, you'll get 8 truck shipments per day.
If your city suffers complete gridlock, you may get down to 2 truck shipments per day.
Solving the problem
If you switch to industry view, and you observe an industry building which never hits 0 freight (empty yellow bar) - then you have identified a building that really needs better freight shipping. Either solve the traffic jams, or place a freight accepting building close to the industry. Watch the truck before you try to solve the problem.
Freight accepting buildings include commercial buildings, trade depot with freight attachment, trade port with freight attachment, many service buildings (power, sewage), and the road out of the city (although I haven't seen that last one accept freight yet).
Step 1: Look at unsold goods. Bulldoze commercial of appropriate wealth levels until unsold goods are close to 0. Now those commercials will be taking in the right number of workers for the goods required. I expect this will free up ~2000 workers in your case.
Step 2: Bulldoze high density industrial... constrain it to medium density. You don't need super dense empty factories. I expect this will free up 3000-5000 workers in your case.
Step 3: Service buildings. Consolidate police and fire into fewer larger buildings. Each building requires workers while the extensions do not require any more workers. Check the number of workers at a service building by pausing the game, checking the city worker count, powering off the building, comparing the new worker count (you can power on the building at this point if you want to keep it). In particular, things like CoalMines and other specialization buildings require a lot of workers. Limit the number of these that you have.
Step 4: Residential density. If it's not all high density yet, you have room to grow. If you're having trouble balancing the traffic of low wealth residential, make a community college or university to upgrade your industrial and focus on medium wealth residential.
Best Answer
The reason for the worker/population imbalance is described in this question. Disregard the population number.
Aside from that, you are trying to balance RCI. This is an ideal goal, but imbalanced RCI also has value as it indicates in which direction your city can grow. When I play, I try to imbalance RCI in particular ways to encourage growth.
Workers vs Jobs
Buildings with jobs activate when the minimum worker count is reached and can accept workers until the maximum is reached. LW LD Industry accepts a maximum of 14 workers (10 low and 4 medium) but will open at full production capacity with any 6 workers. Filling the 8 extra jobs doesn't generate more freight or tax, but it does provide residential wages. This buffer allows your residential to grow without precise management of available jobs. The game tolerates a certain level of open jobs.
Conversely, the game also tolerates a certain level of unemployment. As long as residential buildings aren't running out of money, it doesn't matter whether workers work. MW and HW tolerate unemployment more as those workers earn more money.
In my cities, I tend to keep up to 40% extra jobs for LW. I try to employ at least half of MW and HW, or have up to 40% extra jobs at these levels too.
Shoppers and Goods
Commercial buildings sell goods to stay in business (each good sold generates 1 unit of profit). These buildings also accept freight and sell souvenirs for bonus profit. C buildings can survive and grow just selling goods without the bonus profit, but you need to sell all the goods (check commercial view at 5 am).
Shoppers bring happiness back to residential buildings. Shoppers that visit parks are bringing the same happiness back as shoppers which buy goods, but those park shoppers are represented as unsatisfied in the population detail screen. As long as the residential buildings aren't running out of happiness, you don't need to satisfy all the shoppers.
I tend to satisify 50-70% of shoppers through goods: If there are 1000 shoppers, I'll have 600 goods and 400 unsatisfied shoppers.
Freight and Freight Orders
Commercial buildings accept freight for bonus profit. Other buildings accept freight for no direct benefit to that building. When any building accepts frieght, the industrial truck brings profit back to the industrial building. This allows the industrial to survive and grow.
All freight produced must be shipped (100%). No freight orders need to be filled. An unfilled freight order just means you could add/grow more industrial to get jobs and taxes.
In my cities, I build a freight warehouse to accept freight near the industrial buildings and expand it if I need more freight orders. I don't concern myself with the freight orders of the commercial buildings.