Per meta:Deletionism, few editors use that word as an unironic self-descriptor, partly because it has clear negative connotations. Conversely, "inclusionist" has clear positive connotations. "Inclusionist" in its most literal sense is meaningless to describe any "faction" of Wikipedians as all editors are here to build the encyclopedia until proven otherwise.
Calling yourself an "inclusionist" implies you believe there are "deletionists", a view that many in the community believe runs counter to the idea that Wikipedia is not a battleground.
Attempting to use "inclusionist" as a slur to describe editors who hold this counter-policy "battleground" ideology is not intuitive to general readers of English who are not familiar with niche dispute areas within Wikipedia (which includes the vast majority of editors of Wikipedia).