It all depends on profitability for miners as you said, and we can't accurately predict that until we get much closer to the halving event because it's already exceptionally hard to predict factors that go into calculating mining profitability such as difficulty and the price of the coin being mined. Unless there's some sort of additional incentives created for miners that makes it more profitable to mine on one chain compared to another, the majority of people will mine on the main chain which could be BTC, though I imagine there's also some sort of vested interest involved with BCH or BSV that might skew things.
It makes sense to mine Bitcoin that any of its forks, as it's the most profitable cryptocurrency to mine on the market. This could reduce the underlying security of both BCH and BSV chains as miners would be spending more on electricity than what they'll earn. The situation is worse with both cryptocurrencies' low prices across the crypto market. If Bitcoin-based forks want to survive a 51% attack, they'd need to rely on "merged mining". Developers could allow miners to "merge mine" BCH or BSV with the original Bitcoin (BTC) for added security. But that's entirely up to the decision of both projects' communities within the crypto space.
We'll have to see what happens after Bitcoin's halving takes place in two months from now. All the eyes are on Bitcoin as it's the most valuable cryptocurrency in the world. Both BCH and BSV will experience their first reduction in block reward, which could make things "interesting" for both chains in the long run. Loyal miners will still support BCH and BSV, but those looking for profit will look elsewhere (BTC). At least, Bitcoin Cash (BCH) was able to resolve the dilemma of miners switching constantly between its chain and the BTC chain with the new DAA (Difficulty Adjustment Algorithm). Considering that it's much more actively developed than BSV itself, it might be able to survive a long time in crypto land.
Nonetheless, it's expected that the halving will make Bitcoin and its forks much more valuable than what they are right now. At least, there's hope prices will increase sometime in the future after this dreaded bear market. But people will ultimately decide the price/valuation of each cryptocurrency across the market. Just my thoughts