Others have disagreed, but there's just no explanantion other than they really want the money.
My guess is Lennon's been walking a fine line all summer of begging for the money and trying to keep Celtic fans onside for when they eventually sell.
I think they fancy they can do a lot with an additional £25m and want to rebuild their team to try and pull away from a resurgent Rangers and start getting into the Champions League regularly again.