It is in a sense by design because the focus was creating a decentralize-able/federate-able protocol and infrastructure that can scale more or less indefinitely first and foremost, community second.
The community is working on actually decentralising the network now that things mostly "just work" (assuming you are using did:plc/generally a happy path user).
- Building out PDS communities that are trusted takes time and nowadays there's a few outside of bluesky PBC (one or two big ones and a bunch of smaller ones). People are eager to move off because a lot of users really really don't like bluesky PBC leadership but it's a matter of waiting for these third party communities to reach critical mass.
- Relay infra is already pretty much decentralised. Lots of people still rely on the main relay but it's trivial to use a third party relay and there's more of them than you can count.
- There are a lot of really high quality third party clients and afaict a lot of users do actually use third party clients but there's basically no metric for tracking these stats.
- Appviews are expensive currently and there's work on making them easier to host but there's already one "full" alternative appview for bluesky.
- There are a lot non-bluesky apps/services that are genuinely high quality experiences and they are gaining their own communities.
The main technical barrier to true decentralisation outside of improving UX is introducing other did:methods and/or spreading trust of did:plc across the community (ex: clustered via raft or paxos across major operators) but there's just not a reason to pursue this over the other fires that need fighting in the ecosystem right now (and keeping did diversity low reduces another source of complexity the space just doesn't need to tackle yet).
--------------
TLDR: it is intentional because the goal is to in order of priorities:
1. get the architecture for eventual decentralisation right.
2. make it exist.
3. make it good.
4. make it easy to use for normal people.
5. build community.
6. focus on decentralisation.
Decentralisation in theory is the first priority but in practice it's the last priority. Being able to decentralise is always the utmost importance but forcing it to happen is not ever the top priority because that's on the community, not on the developers.