I feel like you're assuming high-level (or 'experienced') is a good thing.
The highest level players are ones who actually just spam bots all day (as that's fastest xp due to 100% win rate), and are probably actually awful relative to their mmr since they have minimal PvP experience.
Theres also people with 1k games in bronze or silver or gold or whatever (and are hence high level), who are the ones who clearly aren't actually learning from their experiences, so there the relatively low player who might make mistakes is more likely to adapt and learn from those mistakes than the high level who makes mistakes and doesn't learn from them.
Now, maybe you might have a preference on which you'd prefer, but theres reasonable arguments for why someone might have a preference in either direction (I'd prefer the lower level, but you'd rather the higher level, assuming equal mmr), so it wouldn't really be fair for riot to implement something in one direction or the other.