A frequently overlooked aspect in enterprise is billing, accounting and supplier agreement overhead.
In enterprise, Joe developer can often add / use more AWS services and it just goes on the giant enterprise bill, no questions asked.
If you want to use a third party service, waay more work. Supplier assessment needs to be done (by the department that does that) looking at security, company stability, data sovereignty etc. Procurement get involved to negotiate supplier agreement with the vendor and your project needs a specific budget line item which might require a trip to accounting. To get signoff and justify your vendor selection you might also have to do a stupid internal evaluation thing / bakeoff (even though of course you know the thing you really want) where you build feature matrix and carefully adjust the rows so your preferred vendor gets the most ticks.
All this paperwork can take weeks or months.
While a lot of the AWS service offerings are sub-par compared to alternatives, the technical work of papering over this is usually less risky than dealing with all the internal departments which will delay your project if you try to use another vendor.
I think this is a big driver towards bundling being a win for them.