but i then came across some new coins like Swipe, which i'm confident that it does not generate that much in transaction fees, and yet the rewards are high?
Let me explain in simple terms. When it comes to rewards, POS is like POW but you just need to hold your coins. In general, the rewards doesn't necessarily comes from transaction fees alone, the rewards can also include new coins that is being mined from the total max supply of the coins. Though reward distribution method varies from different projects.