[EToS]

At a guess, there are a few things which "could" be working against you:

- Leadership at certain companies can include a lot of people management, and so being in a team of one possibly does make the case for progression in the eyes of HR.

- The company isn't big enough to facilitate career progression for everyone.

- The project may be seen as innovative, but possibly something that will be absorbed into the best practices of all teams over the coming years, and so there may be less of a case to promote anyone in the team because of this. (this is where you need to read between the lines a little, as PO's will omit plans like this for obvious reasons)

- Unknowns.. the people who briefly worked on the team may have raised concerns during 1-1's / exit interviews that you're unaware of.

The best advice i could give is to leave any frustration at the door during the next few months, and keep an eye open for you're dream role at another company.