It's a good question. I did a couple hundred thousand miles on motorcycles (and have the scars to prove it); now car- and motorcycle free and use bikes.

Motorcycles have vastly greater range and speed. So if you need to regularly get somewhere more than 10-15 miles away, and with limited amount of time to get there, then a bike is not a good solution.

But bicycles can use bike infrastructure, are easier to park, can be carried up stairs, involve physical effort which is healthy and feels good. No registration or license. If most of your trips are just a couple of miles (if you live inside a walkable city), then bike is easier, quicker, and more pleasant.

Decent ebikes are NOT cheaper than motorcycles, so that is not a factor.

In places without bicycle roads and lanes where in any case you are forced to mix with car traffic, probably there is no point to an ebike.
Where I live, with fabulous bike infrastructure, I much prefer to be using that, on whatever vehicle, compared to mixing it up on the regular roads.

That's kind of it from my use case.