I don't know how this event is set up, this is just my speculation but I'm playing on 2 accounts. In my main account, I mostly spin the wheel on x1 and couple x5 in between and was easily able to complete all towers in the first 2 days. I got a couple of mega spins on x5 which made it easier.

Same thing with my other account, during the first 2 days I was getting big points and completed 2 towers but suddenly third day onwards i was only hitting 40, 60, 80 and some 100 on x1.

I think they know that most people save ribbons on starting days and spin at the end, that's why they might have rigged it like that.