perhaps because that's installing from a store, not sideloading? however poor (security-wise) the offering may be, you're still using the intended install flow
in this sense i do actually agree about the misuse of 'sideloading' - the planned change would not impact just sideloading, but also 'third party' stores
If anything, the store download is the case where it’s not installing.
There’s nothing “installed” about something which can be yanked from your device or prevented from working at someone else’s whim.