There are probably three main reasons: 1) unified memory (but you can also that with DGS Spark / Strix Halo), 2) access to your Apple account, so you can have a bot handle your iMessages, email, calendars 3) energy efficiency.
Apart from that, if it doesn't work out you still have a Mac Mini, which in itself is more desirable for many than a DGX Spark or Strix Halo if you have no AI use case.
Apart from that, if it doesn't work out you still have a Mac Mini, which in itself is more desirable for many than a DGX Spark or Strix Halo if you have no AI use case.