After seeing the fight play out the way it did I really saw this as Izzy wanting to do the UFC a favour almost, complete a main event for a PPV for them, but only agreeing to do it in a fight that wouldn't be too taxing or damaging for him.
Yoel is a KO threat but he's been badly damaged over the past few years, gotten older, slowed down and does the same thing every fight.
Izzy gets a payday, a title defence, and can turn around and fight a real fight in 4/5 months time. I have no doubt Izzy could have turned up, took more risks and make for an exciting fight... But why bother? If he can keep safe, uninjured, get paid and fight again soon he may as well tick the name off the list and then he gets 6 months if he wants to rest up and skill up.
In the mean time, maybe Costa just waits and gets the shot, or maybe the UFC know he is healthy and ready now and they offer him another fight.
Till vs Costa since they're both ready, winner gets a shot. Cannonier could be back around then so he's another option too.
It's the same reason Henry is fighting Aldo, it's a win, a title defence, a warm up fight and it let's the division build some more heat with other contenders fighting in the mean time.
Henry can probably beat Aldo without too much danger or damage while Yan and Marlon have a war. Then Henry can turn around quickly and fight the winner while he's fresh and shaken off the rust and the opponent is banged up and not 100% but can't really turn down the title shot or they will lose their place.