I'm not sure whether this applies to any other situation other than this BIP66 fork, but since the fork is obviously common knowledge now, one would assume mining pools would exploit any weaknesses.

This weakness is clear: SPV mining pools are building chains which we know are bad. There's no chance of that fork being accepted, like the 2013 fork, so the SPV pools are at a clear disadvantage if they mine blocks with bad headers at the base.

So what is stopping compliant/canonical mining pools exploiting this weakness, thereby diverting (~50%? of the) network hashrate to chains which cannot compete? Wouldn't this explain why the forks keep happening?