The reason is probably that Bluew Wallet cannot simulate an airgapped signer (like hardware wallets which are designed to do this).
You can export the same format xpub/zpub  with Blue Wallet, but cannot sign by reading in PSBTs.

The cheapest option to test is likely a Seedsigner which can work with multiple seeds temporarily.

openoms

96c0b276a3

bitcoin

I'm trying to test out a multisig setup in Sparrow, without having to get a bunch of hardware wallets. I thought I'd be able to just scan a wallet on the Blue Wallet app, on a phone, just for testing. But no, the options are just the standard wallets (Jade, Cold Card, Passport, etc.).

What other options are there, just for playing around with this? I know I could do a software wallet in Sparrow, but that's not quite as "realistic" as I'd like. 

There's the SeedSigner, that could be used too. But is it just not possible to use a phone app?

