RG:
I speak as an insider. There are a great many Chabad shuls that conduct Shalosh Seudos just as in non-Chabad shuls. There are two items that need to be part of the discussion.
1 – Even in 770, where the Rebbe ZT”L conducted a non-meal farbrengen, his brother-in-law, R’ Shmarya Guraryeh (often referred to as the RaShaG) conducted Shalosh Seudos with a meal. I was told by old timers from Chabad that this was the will of R’ Yosef Yitzchok ZT”L, their father-in-law.
2 – Many Chabad shuls have minyonim that are composed of other Yidden who are not from Chabad, and they cater to the practices of their mispallelim. I have personal experience with this, and I am suggesting that this as not unique to my experience.
This explains your empirical data about Chabad shuls. Note that Chabad does not consider Shalosh Seudos a negative thing.