Why?
Doesn't God deserve the best that we can give to Him in terms of worship?
Recall the incident with the woman who perfumed the feet of Jesus.
And the fact that the Temple was lavishly adorned.
Finally, skimping on a Church, which is open to all parishioners, both rich and poor, has been called "stealing from the poor."
Jesus showed his disaproval of the riches of the churches, he turned over the money changers tables. He was against the organized big churches of his day. So they conspired to have him killed. The priests had him killed. They knew he wanted them to change their evil ways.