Compromises had to be made to help Monzo gain market share. I wouldn’t blame Monzo for it, but I would blame the card schemes for allowing the idea of Apple Pay/Google Pay to begin with.
They should’ve just allowed one open standard where the bank exposes an API endpoint and any device implementing the protocol can submit credentials (physical card number + 2FA, or online banking logins) and get back a new card number & the keys necessary to transact. Manufacturers can still call it Apple Pay or Samsung Pay or Huawei Pay but the underlying protocol being open means the banks don’t have to do any extra work (nor even be aware) of any new manufacturers that decide to support the protocol.
I still hope we get there eventually but in the meantime I don’t think supporting every single knockoff payment scheme is a good investment of Monzo’s time. Let’s assume they do support Samsung Pay; what’s gonna be next? Garmin Pay? Fitbit Pay? Badger Pay?