@Reave, the main reason, while perhaps slightly selfish, is that with low odds, the odds of getting fewer encounters than intended gets bigger. (I hope that sums it up best). Basically what I mean is when you have a 1 in 1000 chance to encounter something like a wild wolf, it wouldn't be wildly unheard of to go without a wild wolf encounter for 2000 tries, or even 3000. Knowing my luck, I'd go a million tries without an encounter. It is basically how it works on FR, and after 3 years of no eggs in the coliseum, I just completely gave up on that (and no that's not a battle a day, but a solid 8 to 10 hours of grinding)
With a higher encounter rate, the chances of going without an encounter for so long are a lot slimmer. Yes some will fail, but with the pity token (which I believe was supposed to be called the summoning token), you have still achieved something. Let's say you require 10 tokens to summon a guaranteed wild wolf, that means only 10 failed encounters are required. Or rather, every failed encounter is actually a 1/10th success.
I guess it also has to do with a sense of achievement. As I said, with the pity token a failed encounter is at least still 1/10th of a success, whereas with lower encounter odds but guaranteed succes, basically every encounter that isn't a wild wolf is a failure. A failure that is going to be pretty common.
I get that with the absence of the pity token currently, it is even more frustrating (because we all know what could've been), but I really much rather have semi frequent encounters (which aren't even thát frequent for me, because my luck is horrible), that every 10 encounters guarantees a wild wolf, than super rare encoutners (which for me would mean probably never) but when you do it is a guaranteed wolf.