If a drivechain becomes a threat to the mainchain, it's likely that a significant number of users & stakeholders are benefiting from it. So, the cost of buying miners might be substantial & incentives for such an action would need to be carefully considered.

Why??

If the drivechain employs a different consensus algorithm from Bitcoin's, attempting to control it through miner acquisition might not be feasible & Sidechains, which are designed to operate semi-independently, governance & decision-making processes of a drivechain may differ from those of the Bitcoin mainchain. Thus, the mere act of buying miners might not lead to the desired outcome of terminating the drivechain.