The difference is the incentive to improve, and actual present rate of improvement, for models like this is far higher than it is for jetpacks. (That and certain intrinsic features at least suggest the route to improvement is roughly "more of the same," vs "needs massive unknown breakthrough".)

Trillions of dollars are not being invested in making jet packs any better

Your comparison is incorrect

You say assuming money is limitless and investor patience for returns is endless.

While true, it's the speed of improvement that gives the statement gravity.

> Personal jetpacks are the worst they’ll ever be

Have they become better over the past 20 years?

It's also just wrong. Plenty of things get worse.

Not really. E.g. clay tablets, physical books will not be meaningfully better.

Yes, but they're not going to get any worse.

Books are printed on worse paper these days that doesn't last as long.

"not getting worse" is a pretty low bar

Which is precisely my point. It's the _lowest_ bar possible.