Often builders use some type of composite or plastic resin pad under the equipment that eventually breaks down.
This is what I got. 2 precast concrete squares. Roughly 4X4. One for the heater and one for the pump/filter. 7 years later they are showing signs of breaking down/crumbling in spots. But they were $100 each so they saved a bunch over having a quality poured pad. I’m undecided if I’ll just replace them once they go or put an actual pad in. I’ll be doing it myself and getting the new pad to the right height to match the plumbing may be trickier than I want to tackle.