Because there's 365 days in a year (duh). I mean, if it were, like, 200, then a year would be 0.7 season cycles?

Same for a day. If we set it to, say, 10000 minutes or whatever, noon could very well end up as the middle of the night eventually.

As for the minute and hour, how else would you fit seconds into a day? 24*60 square rooted for equal units? So we have 120 new minutes each 120 seconds long? I mean, I could see that sort of working? But it's still pretty weird, and not a true decimal. So I guess you'd have to rework seconds also.

Edit: months are based off the moon, and there would be no way to somehow make units of 10 months fit into a year, which literally cannot be anything other than 365 days, unless you want your afternoon tea parties 0.12 daylengths past midnight.