Let's say someone created a centrally managed sidechain, received 1M BTC as 1M scBTC on that sidechain, but then artificially increased the supply of used scBTC on that sidechain to 10M scBTC over time.
Someone would need to come up with one hell of an explanation to incite people to transfer 1M BTC to a centralized sidechain.
This doesn't seem to me like a scenario that sidechains introduce. On the contrary, now that they introduce the opportunity for any one to set up decentralized platforms, proponents of a centralized scheme would be hard pressed to explain their reasoning behind the creation of a centralized structure on top of a natively decentralized sidechain.