if the scBTC can take advantage of faster tx times, why not?
miners would like it too as they'd get all those sources of income, tx fees from scBTC and sidecoin, as well as block rewards of sidecoin.
Because users have no interest for a sidechain with an additional sidecoin. Users will go for the more safe, most risk-averse chain which is the scBTC 1:1 peg model
but the SC would be MM. just like Namecoin is today with 70% of the Bitcoin hashrate.
Only largely accepted and used sidechains will be mined because only those will have value. As I've stated many times, miners will not MM speculative coins or other obscure schemes that gain little traction, there's no incentive for them to do so.
A sidechain using both scBTC and issued assets (sidecoins) for whatever reason is simply inferior to the superior scBTC 1:1 chain. To serve monetary functions ex: faster transactions, the appSidechain or as I have called them, utility chain, is simply the more logic choice.