Why there is no RGB MVP with updates rolling out after?

Firstly, it depends on how one defines 'MVP'. If by that one means RGB being released as a token protocol, then the answer is simple - it is not a token protocol thus cannot be released as one. Though issuance and management of highly scalable, programmable and private assets of different sort is possible with RGB, it can be applied in many industries far beyond financial world.

To explain further, RGB is a technology built around the concept of client-side validation, and the latter, by definition, is a much more restrictive environment than blockchain or classical programming ones in terms of protocol updates and such, making things like 'MVP' impossible and making no sense. At the very beginning of RGB active development back in 2019, Peter Todd made a strong suggestion that was accepted by all involved parties, that the protocol will be released as one version and this version would be final. If some additions or changes will be required, due to the client-side validation nature of the technology, it will lead to creation of a whole new protocol, not-compatible with existing version. So, there are no plans (and in fact - not technical possibility) to have an MVP of any sort and adding different functionality afterwards.