They didn't pass on him.
Kessel picked where he wanted to go and Kessel picked right. Are people forgetting the guy had a NTC and vetoed other teams but chose the Pens?
Chicago, l.a, minnesota, Montreal, Philadelphia, Boston, nyr, pittsburgh
These were the teams reportedly on kessels list.
I don't remember him vetoing any trades.. there was never a rumour of the leafs approaching him and asking him to accept a trade to a team not on his list, and him vetoing it.
Also Kessel himself said he'd accept a trade, as he likes Toronto but doesn't want to play somewhere he isn't wanted.
He had a list of 8 but there wasn't any indication of him wanting to "pick his spot". Pretty sure I read that there wasn't a big interest in him, the Pittsburgh deal was the only offer. I'd have to dig to verify this, maybe other leaf fans recall.
Here is a Simmonds podcast where there wasn't much interest in Kessel besides the pens. I'm not going yo watch it but I'm sure it'll just verify what I thought I heard at the time of the trade. Pens being the only team seriously interested.
http://www.tsn.ca/radio/toronto-1050/simmons-not-much-interest-in-kessel-besides-pens-1.323676