Time and modern influence. Plus the fact that Jesus was explicitly fighting against ‘repent and be saved’. The lessons are right there in the gospels but most people do not really dig into them and so they don’t really understand what Jesus was teaching.
‘Repent and be saved’ was how prominent Jews of the day saw their relationship with God. Jews had the laws, the covenant given to them by Moses, that ensured they stayed in the good graces of God. This covenant, among other things, specified the necessity of animal sacrifice at the Temple, formerly the Tabernacle before the Temple was built.
The theology involved was ancient, the Old Testament chronicled more time before Jesus than has elapsed since. One of the major plot points in the gospels was Jesus railing against a literalistic interpretation of the Word of God. Jesus redefined righteousness to mean more than mere adherence to Biblical law.
You need to understand the spirit of God, not just follow laws like an automaton. His telling Christians that they could eat pork, that they didn’t have to follow ancient dietary practice, was deeply unsettling to Jewish elites and the reason they got him killed was because he was challenged their way of life so.
‘Repent and be saved’ is recognizing that you are sinning against others and the Lord by eating pork. It’s precisely what Jesus fought against.
Of course, legalism is an ancient human impulse, Jesus didn’t force anyone to stop being legalistic, and so individual Christians and whole congregations and even entire denominations will misrepresent Jesus by teaching literalist interpretations of scripture.
But this isn’t what Jesus wanted. Enlightenment is closer to what Jesus wanted than incessant repentance. So many modern-day spiritual seekers will find Jesus more in line with Buddhism than with modern-day Christian interpretation of theology, for good reason.