At times in one of my pools, the better players will start using small bets preflop- and sometimes from all all positions. Why are they doing this and how do I best deal with/exploit it? Further, they'll then underbet the flop to something like 25-40% pot.

For example: In one of my 10nlz games, .22 and .28 are common OR sizings, and again - many of these players will use this same size from all positions. Again - why are they doing this and what is my best approach to calling/3betting? Naturally, I see my VPIP and PFR gap increasing in games like this, even when I'm 3betting ~10%. Is this ok? Then, when dealing with the flop, we see the aforementioned underbet IP. What is their strategy here and is it sound? Can I exploit this approach easily?

Thanks!