Mining appears to be profitable because of Bitcoins price increase. It is not profitable solely based on fees as intended. Various forks have actually tried to mess with the fee structure IMHO, with other second layer solutions that do not or try not to pay yhe necessary fees it takes to sustain it beyond price inflation and scarcity cycles. DC would give a sustainable fee environment, something the community actively dislikes based on recent fee increases.

The lack of adoption for other sidechains is directly tied to their design. Is there not demand for zcash ? Ethereum ?

The structure of DC is unique in such a way that the frictions of alternatives do not exist.

The other "sidechain" proposals make tradeoffs in areas that DC does not, at the expense of time. ( instead of final settlement being within the regular network time, as with something that has third party liability like Liquid, DC counts for 6 months in public)

Drivechain supporters claim and can prove that through BIP 300/1 all the demand for anything in crypto outside of Bitcoin, is the demand we would see with nothing but a smooth Op_drivechain between it and Bitcoin.

anti-drivechain advocates will claim this means "we want shitcoins on bitcoin" , but a more accurate statement would be "shitcoins don't exist, only worse and better ideas". Those worse ideas might aswell support the main network and for low cost of a soft fork, we get to implement any good idea that might come along in a safe way. (Zcash sidechain, eth sidechain)