The monasteries were very rich, and he did need money.
But this is the thing - there's no reason to assume that being Catholic automatically means you support the monasteries. It would be perfectly possible for Henry, or perhaps more realistically Henry's advisors, to have persuaded him to reform the Church and close down a lot of monasteries, and for him to have continued as a perfect Catholic king.
In bits of Europe that remainded Catholic, this did happen - lots of monasteries were rigorously reformed. And people have been arguing over monasticism as a way of Catholic life for centuries.
I think (and this is now getting too late for me, and I'm hazy) that there may be some connection between what look to be increasingly stringent laws against begging/vagrancy in Elizabethan England, and the closing of monasteries.