What makes you say that? I would guess they would do both if it was worthwhile. Android tablets and iPads have different capabilities under the hood - maybe the requirements aren't possible on Android tablets?
In any case, saying their priorities are misaligned because they don't scratch your particular itch is making a mountain of a molehill.
It has nothing to do with device capabilities or technical effort, and there are client forks which support it. Signal have simply made a conscious choice to disallow it.
MobileCoin is prioritised ahead of allowing an iPad-like secondary device experience on Android tablets, for example.