We use the ELO rating system https://en.wikipedia.org/wiki/Elo_rating_system, which is quite common in games.

What it does is that as you move up the ladder, you get fewer trophies for winning and lose more trophies for losing. The same rule applies to all other players. It's not possible to let everyone level up all the time, so the higher your rating, the more difficult the matches and opponents should be.

In very rare cases, if the rating gap between opponents is too large, the game may not reward you with any trophies at all. This should not happen very often, so do not worry about it.