The entire back-end has changed.

Literally. People miss the fact that Steam is still a 32-bit app just to support older games. The rest of the world has moved onto 64-bit operating systems and applications. It's shocking they still support 32-bit in 2025. So the argument that they aren't supporting older titles is a little misleading because that's the whole reason they still run a 32-bit client.

Most operating systems are no longer even offered in a 32-bit variant, 64-bit only.

I haven't had a device with 32-bit hardware in almost 15 years. The last device I can even think of that was still 32-bit within the last 15 years was a Google Nexus 6 in 2014. All the Pixel line have been 64-bit.

Steam is literally one of the last 32-bit holdouts. Everything else has moved on. Even Discord dropped 32-bit support last year.

EDIT: Also, for reference, since Windows 98 is heavily mentioned in the arguments, those operating systems included 16-bit code. We're talking about dropping 32-bit code, 16-bit code is deader than a doornail. Windows 3.11 was the first introduction of 32-bit code. Windows XP seems to be where they dropped all 16-bit code in 2001. We're talking over 30 years of hardware changes.

All versions of MS-DOS and the below versions of Windows had 16 bit code:

MS-DOS (all versions)
Windows 1.x/2.x/3.x (all versions)
Windows 4.x or 9x (Windows 95/98/Millennium Edition) (all versions)