If you don't have a basement and the builder didn't want to put a cover plate in a closet somewhere, the attic is the only place left inside.
It is very common for a builder to simply run the low voltage wires and leave them un-terminated. A builder can say "wired for cable\internet" without any terminations being made. Hopefully there's an outlet somewhere up there because you'll need power for the router and if you're lucky there's a breaker you can toggle instead of having to climb back up there to reset it.
If you find coiled lengths all piled-up in some location, the builder might have planed on dropping them down one of the walls, otherwise have fun making all the connections hunched over in your attic and dealing with having equipment up there.
Why are most of my cable/coax wires disconnected?
This would be no different than many people's basements I've seen.
Do I unplug the CATV Link and hook it up to the router/modem?
Going by the installation guide for the distribution panel, the jacks labeled "CATV Link" and "SATV/CCTV" are passthrough ports that go to the back of the panel, meant to be used for satellite. I can't tell from your photos where, if anywhere, they go in your system. The input to the 8-way splitter that feeds the TVs is also on the back of the panel.
The recommended thing to do is to disconnect the cable going to the splitter input, and connect it to a two-way splitter (perhaps you already got one with your modem, and perhaps it says that one side is for the modem and one side is for TV — if so, use it, and follow the instructions). Using short cables, run one output of the splitter back to the distribution panel input and the other to the modem. Possibly you already have such a splitter and one or both of the passthrough ports are connected to its outputs? If so, then you could connect the modem to one of them without re-wiring anything, but I can't say.
If that's not possible (for instance, not enough space or available cable length), you can try connecting the modem to one of the other outputs of the splitter (unplug one of the cables going to a room, connect a short from the panel to the modem, optionally add a splitter to restore service to that room), but the modem may not appreciate being downstream of an 8-way split.
Then there's wiring for Ethernet. I can see that the cables running to the Telephone Distribution Module are Cat5 or similar; are they terminated in RJ-45 (wide, 8-contact), not RJ-11 (narrower, 4-contact) jacks in the rooms? If so, then yes, you should be able to pull them and plug them into the cable modem, and the patch panel wouldn't come into play.
But if there are cables going into the back of the patch panel running to each room — perhaps the rooms have separate "telephone" and "data" ports? — then you're better off getting 6" or 1' Cat5e patch cables, and connecting the LAN ports of the modem to each port of the patch panel, and lighting up the data ports that way. That seems more standard than using "telephone" ports, but I guess who has landlines these days anyway?
Finally, a note about WiFi. Is your cable modem/router also a WiFi access point? If so, you might not get the best signal with it closed up in the wiring closet. If it works there, great. But if it doesn't, then there's another way you can go:
Buy an inexpensive Ethernet switch with as many ports as the number of rooms you want internet in.
Place the cablemodem in a room with coax and ethernet ports, where it will also be in a good place for WiFi reception.
Hook up the coax splitter as before, except instead of running one of the outputs to the cablemodem inside the wiring closet, disconnect the coax for the room with the cablemodem from the 8-way splitter, and connect it directly to the two-way splitter. Or if you had the modem connected to one of the outputs of the 8-way splitter anyway, then just leave the coax the way it was when you got here.
Connect the cable modem to the cable jack in the room where it is, and connect one of its LAN ports to the Ethernet jack in that room (you can use any other LAN ports on the modem for more devices in that room).
Put the Ethernet switch in the wiring cabinet, and connect the cables for all of the rooms that you want Ethernet in to the switch. If the switch has a special "uplink" port (it probably doesn't), connect the room with the cablemodem to that port. Otherwise, just connect it to any port of the switch.
Last, but not least — you seem to have really nice structured wiring in the house, but your panels don't have any labels on them. As you hook things up and you discover which ports and cables go to which rooms, write them on sticky labels and stick them in the slots provided on the side of the panel. It will be good for your sanity later on.
Best Answer
Summarizing what has been said in the comments:
Having the blue pair paralleled between all the cables strongly suggests the builders intent was that they be used for phones. Cat5e cable is often used for phone wiring as it's more interference resistant than regular phone wire and the blue pair is the conventional "first pair" for phone wiring.
As for your options, there are two main ways forward.
Option 1, ditch the phone wiring cut off the builders mess and terminate the cables individually as network cables with all four pairs. This will let you run gigabit networking.
Option 2, leave the phone wiring as it is and use the green and orange pairs of each cable for Ethernet, this will limit you to 100 megabits per second.