Inbreeding in the OT (marking this NSFW just in case)

I am doing my first “Bible in a year” program and I am really enjoying it— it is a great use of free time and I find myself spending hours reading different translations, taking notes, referencing theologians for further understanding, etc.

I’m a bit confused: I initially assumed incest in the OT was out of necessity due to how few people were on earth at the time. Adam and Eve’s offspring would have to procreate with each other because it was the only option.

It also made sense when Lot had children with his daughters, because (in my understanding) they believed there were no other survivors after the destruction of Sodom and Gomorrah.

It did not make sense, however, that Rebekah sent Jacob to her homeland specifically to marry a relative.

So… what’s up with that?

Additionally, a question for those who affirm Biblical inerrancy: why were there no apparent repercussions of inbreeding in Genesis, when the issues that face children born out of incest are observable today?