Good question. You're right that it's tough to win the pot unimproved with these small pairs postflop, so you have to consider other potential sources of value. As others have pointed out, it's going to be -EV to open shove 20BBs with 22 UTG, so don't do that. 

If you choose to minraise a small pair, most of the value will come from stealing the blinds, so you need to assess the likelihood of that. A guy could make a couple of videos on that subject, so it's too much to get into here.

Also, although you might generally be planning to fold to a 3bet, there may be a few short stacks at the table you can profitably call. This makes a small pair a better bluff-raising hand than some other cards you'd otherwise be folding. 

Finally, the fact that you'll sometimes flop a set does increase the value to you of seeing a flop. So if you think there's a good chance BB will call you, and there often is if you minraise, then you're better off going for a steal with 33 than with K5o. Even if you generally give up postflop, just having the chance to flop a set increases your equity considerably.

In short, raising with these hands from EP will mostly be a bluff, but that doesn't mean you shouldn't do it, because they are often among the better bluffing candidates.