Please delete if improper.
Have not seen lately those temporary spare tires in new vehicles. Has it been a reversal ? Are they proven inconvenient ? What happened ?

 

I've seen 'em, they just aren't as common anymore. The big reason for this is fuel economy. More and more manufacturers are replacing the temporary spare with an air compressor and a can of Fix-a-Flat (or equivalent) because a tire and jack are heavy. Removing them removes like 70 lbs, frees up space for more storage, and improves mileage due less weight.

 

Most AWD systems require continuity across all four tire diameters to ensure that all the spinning bits are synchronized. This is the reasoning behind not locking your center diff on pavement, and is illustrated when making tight turns with it locked. The inside wheels rotate slower than the outside wheels and this strains the driveline. The same thing will happen with a spacesaver tire at one corner. That tire will spin faster than all the others due to its reduced diameter and you will damage the driveline. With more and more vehicles on the road being AWD spacesaver spares are no longer as compatible. All that said, I have no idea if the claim that there are fewer on the road is true but rest assured that whatever decisions were made by the auto industry to solve the flat tire conundrum, it was to reduce cost and improve profit margin.

 

I'm not a fan of this trend, my Kia Niro has an air compressor and a can of "fix-a-flat" even though there is very clearly enough space to have a donut spare, and the car probably does have it in certain markets. While the AWD reason cited above is certainly true, my old Subaru had a fuse you could undo to uncouple the rear wheels from the AWD system (I'm sure the fuse just sent power to the clutch pack) and turned it into a FWD vehicle for just such occasions, it even illuminated a "FWD" lamp on the dashboard. I only had to use it once, but honestly I'm sure I'm one of the few folks who actually reads the manual to their car and this technique probably is unknown to your average driver.

But the thing that really sticks in my craw if that most places wont patch a tire in which fix a flat has been used so you have to buy a whole new tire even if it's a fixable puncture, or in the case of an AWD vehicle a whole new set of tires! I'm kind of surprised a modern vehicle can't use wheel speed sensors with other sensors to tell that a donut spare is fitted and disengage the AWD system automatically so you can have your flat repaired and remounted.