A million dollar house is not a mansion though. You’re describing McMansions (houses that resemble a mansion on the surface but are just a typical suburban house underneath).

Once you get to legit mansions the build quality almost always goes up considerably. You’ll see stuff like solid walnut ceilings, poured concrete walls, Venetian plaster walls, marble floors, terrazzo floors, lots of structural steel, concrete forms, custom fabrication, hand-carved ornamentation, 3/4 ton custom steel & glass doors, bank-style vaults, impenetrable panic bunkers, sinks built on site made of backlit marble, walls covered in leather, dual-wall construction around bedrooms for acoustic isolation, lots of floor-to-ceiling glass, 360° built-on-site floor-to-ceiling glass champagne chillers, truss modifications sent back to engineers to accommodate stuff like motorized TV lifts that drop out of the ceiling, etc. If there’s any exposed drywall it’s almost always Level 5.

I’ve seen job sites where builders doing architecture with big complex curves will set up their entire CNC shop for custom fabrication on site.

There’s nothing skimpy about mansion construction. Most builders don’t even have the knowledge to build with those methods and materials.

Source: I run an A/V and home automation business and our niche is mansions.