I'm actually not sure and can't find any information on that but if I were to make an uneducated guess, it would be that the statues themselves weren't really a part of the original building plan; just the spots for them were with the expectation that they'd be added over the years like art on the wall would be.

But again that's just a complete guess so take that with a grain of salt

I would posit that the original statues fell or were pulled down