I have a number of good friends, some Ashkenaz and some Sefard, and there are plenty of “intermarriages” between the two groups.
But the comparison to MO or chassidus is a faulty one. An Ashkenaz person and a Sefard person who went through the same or similar schools are likely at a similar level of observance and hashkafa (every individual is different, of course, though) so you would expect shidduchim between those 2 groups would make sense. But to compare that to an MO or Chassidic person who went to very different schools and/or has very different hashkafos, is ridiculous as one would need to adopt a very different STANDARD of observance rather than adapt to slight differences in the SAME LEVEL of observance.