Please stop messing with the Scale commands?

The preference was added some time ago.

You can also switch the current proportional scale setting in the options bar, when Free Transform is active.

As to why it was changed, a lot of things have changed over the last 20 years. One of those things is that people started asking why we should have to hold down Shift if we want proportional scaling most of the time. So across the industry, more applications — especially newer ones — now default to proportional scaling, only requiring Shift when you want to distort. In other words, if someone decided to drop Photoshop over this issue, now their problem is that many of the Photoshop competitors they could switch to actually work the same way! The other reason Shift was dropped is because of mobile apps; they default to proportional because there’s no Shift key on a touchscreen. Now everything is more consistent across devices: Proportional by default.

The main remaining problem is that other Adobe applications still require Shift for proportional scaling, so this behavior is now very inconsistent across Adobe applications.