How would that make any sense though? The longer a climb (or the longer you are climbing) the more likely you are to fall.
But if you wanted such a system you would have to do something like you can climb a distance equal to your climbing speed x your proficiency bonus.
So, with a speed 30, your climbing speed is 15.
Without proficiency, you make a check every 15 feet.
With proficiency, you make a check at 30 feet (+2), 45 feet (+3), ..., 90 feet (+6).
Thus, for a 60 feet cliff, without proficiency you would make 4 checks, but with a +4 or higher proficiency bonus, you would only make 1 check.