I do understand, I've given up on a very popular game myself (Melody) because it made me pick. But in that case I simply didn't consider that game good enough to deserve multiple playthroughs.
The way I see it, between playing a harem game twice and playing different routes for the same non-harem game, the first option has the disadvantage of repetition. We're wired by nature to prefer new and different experiences.
Why I do really dislike is when a game doesn't warn you in advance that picking an event with a girl will make you not able to attend one with another girl. That's ugly and has caused me to delete those games.
But indeed: different strokes for different folks