We are being way too judgmental. The King of Thailand is the richest monarch on earth (that's what I read).
He has donated millions to other charitable causes and this is just one of his many gifts.
The greater beauty of the monument will lure more tourists which will help the local population who are really, really poor.
There is so much opportunity to make merit in that area by helping the locals who are in extreme poverty. You would think all the Buddhists there would help them. But alas no. We like to criticize others, but when it's our turn we fail.
Let us keep our eye on ourselves and what we do and not do.