big design uses few resources

I compiled a design a few days ago with a Compilation Report like this:

Combinational ALUTs 52,437

Memory ALUTs 0

dedicated logic registers 31,310

Total registers 31,310

...

Total block memory bits 456,312

Today, I compiled a similar one with some IPs added. When I finished the compilation successfully, I got a Compilation Report like this:

Combinational ALUTs 671/650,440(< 1%)

Memory ALUTs 0/325,220(0%)

dedicated logic registers 1187/650,440(<1%)

Total registers 1187

...

Total block memory bits 6,200/23,685,120(<1%)

I don't know why this happened. The design occupied too few resources. Can anyone tell me? Thanks a lot!