When you're using a modern browser that browser will require any certificate to have a certificate transparency log stamp. Certificate Transparency logs are public append only logs of issued certificates.
So you access example.org. Your ISP uses the compromised CA certificate to create and sign a rogue certificate for example.org. It now has to submit this certificate to a public certificate transparency log and gets back a proof for that. Now it can use that rogue certificate and the proof that it's in a CT log to impersonate example.org and MITM your traffic.
CT does not prevent compromise, but it makes it far easier to detect. If the people behind example.org have a look at the CT logs they will see the rogue certificate there that they did not request. This makes rogue certificates and by extension CA compromise detectable. So your ISP cannot just do this forever in secret.
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When you're using a modern browser that browser will require any certificate to have a certificate transparency log stamp. Certificate Transparency logs are public append only logs of issued certificates.
So you access example.org. Your ISP uses the compromised CA certificate to create and sign a rogue certificate for example.org. It now has to submit this certificate to a public certificate transparency log and gets back a proof for that. Now it can use that rogue certificate and the proof that it's in a CT log to impersonate example.org and MITM your traffic.
CT does not prevent compromise, but it makes it far easier to detect. If the people behind example.org have a look at the CT logs they will see the rogue certificate there that they did not request. This makes rogue certificates and by extension CA compromise detectable. So your ISP cannot just do this forever in secret.