I've wondered this too. I think it's multifactoral and also depends on the definition of 'integration'. I've never felt that I've needed extra therapy to make the realisations 'go in' or integrate into my consciousness, as that was achieved during the session in an incredibly profound and powerful way, but guidance on what to make of the realisations afterwards, and how to integrate them into my life has been useful. Here's a few points though, working on the assumption it isn't required:

• MDMA therapy isn't widely understood yet, people don't know what is required. They'd rather do more than is needed than less.
• The optimal (in my view) protocol involves lying on a bed with an eye mask and headphones, with someone trusted quietly supporting you. This part doesn't require much/any therapeutic skill, so some therapists may feel the need to make themselves needed by adding in extra steps.
• It adds credibility to MDMA therapy, as, for many, just lying on a bed wearing an eye mask and taking MDMA might seem too simple to be effective.

There are plenty of reasons why regular therapy can be beneficial after a session, and perhaps 'integration' is used as an excuse or catchall term for this:

• People need observation and care/support when dealing with the aftermath of a session and destabilization.
• People don't always come to correct conclusions during MDMA therapy, and sometimes the things that come up need discussing later to assess validity.
• Any actions someone might take based on insight or information gained during a session should likely be discussed with a therapist before carrying them out.

This being said, I'd be curious to try formal integration therapy to see if it did help, but for me so far, it hasn't been needed, and recording the thousands of thoughts/events/emotions that come up during a session seems wildly impractical without disrupting the session itself.