Flavor – Why does garam masala powder taste bland

Two properties of salt that oregano doesn't have:

water solubility: you drop salt in water, you put it on chicken, you put it in tomato sauce. Most or all of it ends up dissolving, making it easier to mix.

osmosis: related to above. Sprinkle some salt on raw meat. Come back in 5 minutes and you'll see beads of liquid on the meat, almost like it was sweating. That's a combination of salt dissolving into the liquid on the surface of the meat, and osmosis pulling less salty water out of the cells of the meat to balance the salty water on the surface. In 10 minutes, some of that liquid will have disappeared. Part of this might be due to evaporation, but part of this is due to the liquid pulling salt into the cells, which changes the equilibrium and allows for the cells to draw liquid back in (principle behind brining meats).

Salt has a natural way of penetrating organic matter that oregano and many other seasonings don't. There are other mechanisms at play too--salty foods can make you salivate, which may make something feel "juicier" in your mouth. I'd highly recommend the Good Eats episode on salt as a start.

If we're talking about a solid, four pound cut of beef - the only flavor you're ever really going to get is on the exterior and just a little bit into the interior of the meat.

That said, cooking in the spices/components you list still may provide liquid gold. I would simply take some of the liquid that's leftover in the slow cooker after the roast has cooked and make a gravy out of it. You'll get the flavors you put in and have something to sauce the interior of the meat - that have been flavored with the juices of the meat as well.

Otherwise, if you're looking to 'infuse' more flavor into the beef itself, you'll need to consider something like a stew rather than a whole cut.