Besides the fact that they are not, we should be quite cautious about scope creep and the mandates of particular collectives. The Ecosystem Tech Fellowship that I had in mind mentioning here is quite different to the Core Fellowship. There were a few meetings/forum threads about this but it never came to fruition (although would still like to see it).
You are basically saying, “the members of those two groups are developers, so let’s combine them into one group.” But they bring different knowledge, experience, and perspective. The Core Fellowship has experience in the core Polkadot protocol, why things were designed and implemented the way that they were (because they quite literally implemented large amounts of it themselves), and thus can understand the consequences of modifying certain parts of it.
A Parachain Technical Fellowship would bring experience more focused on running a parachain on Polkadot and the challenges associated with it. They might use their power to unbrick parachains (a matter in which the Core Fellowship would want to stay neutral) or their Treasury to fund block explorers for all parachains.
Comparison: You are a lawyer, so surely you can help me with {my problem} in {my jurisdiction}, right?
Yes, separate entities has added costs, but a collective’s mandate to the network should be clear, and not one of convenience. Things that are not within the mandate of any existing collective should go through public referenda, and a large number of similar proposals to public tracks would indicate that a collective dedicated to that area of expertise may be worth the cost in order to reduce the noise coming to public tracks.