Why exactly we have to rebuild the bundle when updating Unity?

Preface: I was talking about our bundle issues with a colleague and I said our main problems are with needing to update them every time Unity comes up with an update. Then he came out with the pretty straight forward idea that if bundles didn’t have scripts in them, they wouldn’t need to require a bundle update.

So…

If the current requirement to restrict and tie Bundles with a very specific Unity version is due to that, wouldn’t it be a good idea for Unity Team to make it possible making script less Bundles which wouldn’t require updates with every single Unity update?

Is this even the sole reason why we are enforced to update bundles along with Unity releases?

Its because our mobile bundles do not contain type tree information. It is however something that will change in the future.