How did Christianity diverge from Judaism and Islam on the topic of eating pork? It's the only one of the major Abrahamic religions that's okay with it, which seems pretty odd given their common lineage and the fact that it came into being after Judaism/before Islam.

The answer that's already been linked is really good, but there are some details I can add re: Christianity.

Food taboo is a fundamental part of the ritual purity system in the Jewish tradition. Its form in Torah dates to before the exiles, but in the Hellenistic and early Roman periods it was gaining major prominence as a means of identity formation, because Judea was gaining a growing non-Jewish population, and because outside of Judea it was a visible way to set oneself apart from the gentile locals. Pork became the quintessential example because it was a relatively affordable meat and therefore one that Judeans could point to as stereotypically "gentile" food, so avoidance of it became a solid way for Judeans to assert their Judean-ness (Kraemer talks about this in Jewish Eating and Identity through the Ages).

Cool, so what about Christians? People, including scholars, like to focus on Jewish tradition when they're looking at early Christian development, and while that isn't wrong, it leaves out the fact that from a very early period, Jesus worship was finding a lot of its adherents among non-Judeans. Our earliest sources are Paul's letters, which are exclusively written to non-Jewish Jesus communities. And while Greeks and everyone else had ritual purity systems just as robust as the Jewish one, widespread codified food taboo was unique to Judea. The go-to book on Greek ritual purity (Miasma by Parker) has a short appendix on food that basically says that there wasn't an overarching system even on the local level.

So you have a movement that emerged in Galilee/Judea and is based in Jewish practices, but is spreading among people who don't necessarily have any particular need to identify themselves with Judeans writ large, AND don't have stringent ritual taboos around food as a basic cultural expectation. Plus there are a lot of questions about how much early Jesus followers cared about differentiating themselves from other gentiles. Most of our authors care about it a lot, but outside of that it's difficult to say, and there's evidence that at least some people weren't bothered about it.

Where you do get taboos around food in early Christianity is on the issue of meat that's been sacrificed to non-Jewish gods. Some Christian groups were fully vegetarian because of this issue, but it was a pretty heated debate. I've never encountered a source that cared what species the meat was in that context, just whether it had been sacrificed.