Why did you decide to switch to a new camera?

Ive gone through Nikonos V to housed film SLR to housed DSLR that is 15 years old now. I am finally going to move to a new system. Important to me is bulk/size and an excellent viewfinder with 100% view. I am on the fence sticking with a DSLR or going mirrorless. From what I have learned, at least in the Canon ecosystem the mirrorless lenses need more time to mature and catch up to the quality of L series EF lenses. So I may go with a 5DIV housed since I have the lenses and camera already vs buy into a whole new ecosystem like the Sony A7R III. Would love to here what others think?