They are. See Zcash Shielded Assets -- Asset Swaps and beyond
Once vanilla ZSAs are deployed, the next step is to enable asset swaps. Once that’s in place, Zcash becomes a private, trustless, permissionless settlement layer, which is the hard part of building a non-custodial DEX. Counterparty (and price) discovery can happen offchain, with the trades settling on the Zcash network (effectively replacing the role of a central counterparty in the traditional financial markets).
Anyone can then build an exchange (centralized or decentralized) on top of Zcash that enables the trading of any asset that is issued as a ZSA (or gets bridged to Zcash from another chain).
That’s a game-changer for DeFi in general, never mind Zcash.
Imagine if Zcash became the default settlement platform for DeFi trading? 
Some perspective might be useful here.
From Q4 2020 (when the Dev Fund started) thru Q4 2023 (the last published quarterly report), ECC spent $24.5m, or an average of $628,769 per month.
So, this research and design grant is roughly equal to one month of ECC’s average burn rate.
I grok this argument. However, I think it’s worth exploring this space as a means to better understand the trade-offs and implications. In the process, we may discover solutions that we can’t conceive of today.
Everyone in the Zcash community had the opportunity to provide feedback, and indeed, as has already been pointed out, @joshs did.
With that said, we can all do things better going forward, in terms of ensuring that core developers are aware of grant applications relating to protocol development.
However, to be clear, the fact that we can do better going forward does not mean that anyone did anything wrong in the past. Growing the ecosystem isn’t easy. There’s no decentralization fairy godmother. We need to be prepared to put the effort in, and collaborate to make it work.
I also grok the protocol complexity and risk argument.
However, it could be deployed in a separate pool (notwithstanding the anonymity set tradeoffs). Hell, it could deployed as a sidechain, to keep it entirely separate.
There’s a whole design space we can explore to see if these risks can be mitigated.
And if, after doing the research, and exploring the design space, we conclude that the downsides outweigh the upsides, and end up discarding the idea, that’s fine. Research has value, even if the answer is “No”.
ZCG approving a grant doesn’t automatically imply that any new functionality resulting from that grant will be deployed on mainnet - the community still needs to reach consensus on changes to the protocol.
Maybe we need to explicitly recognise that it’s an important part of the core Zcash engineers’ role to provide feedback on these sort of grant applications, and to engage with and support other teams entering the Zcash ecosystem.
If that means that less time is devoted to other work, then so be it. The importance of growing the ecosystem and making it more decentralized cannot be understated.
We should be welcoming and encouraging innovation, not stifling it.