I'd say it's marketing strategy.
"Tendo is here, go get him!"
They're teasing and tempting players who are close to have him to spend and get him.
I have a few thousand cps I've been saving for a long time. I was so tempted to spend but nah I'll hold and hope there will be another event he might be cheaper. :P
I've spent a bit on that wheel because there, more or less, medium refinement costs 15 coupons. With 1500 coupons i gained the 100 redeemable ones + 3 seal scrolls and 11 summoning scrolls. 5 Ay fragments 0 tendo, sadly, but doesn't matter. I don't think they were wasted but only due to how relatively cheap medium refinements are there.