Why did PS decide to have Shift Key and Scale be non-proportional???

It’s important to notice that in newer desktop and mobile software, scaling is proportional by default, so people now learning photo apps for the first time are used to not having to press anything to scale proportionally…it’s the default, which makes sense because proportional scaling is what most people want most of the time. This is even more important on tablet/phone photo apps, because on those touch devices there’s no Shift key to press anyway. It looks like they made Photoshop more consistent with the latest best practices.

The complication, as you’ve discovered, is that other old apps haven’t adapted. Other applications created during the early years of personal computers 30 or 40 years ago, such as Illustrator and Microsoft Word, still require the Shift key to scale proportionally. So we have to deal with apps from the same company that have different scaling defaults.  

If someone thinks about switching to a competitor because of this, the big problem with that is: At least two of the major Photoshop competitors I checked also don’t force you to hold down Shift to scale proportionally, you just drag a corner and it’s proportional…they adopted that default before Photoshop did! So industry momentum is toward the simpler, easier proportional scaling by default, and what needs to be done is to update the oldest apps like Word, Premiere, and Illustrator to catch up to how things work now across the industry.