slang terminology like "fixie" comes with alot of baggage and ages poorly - and with any trend, baggage will add up and it will get old fast. "fixed gear" while awkward in speech is more neutral and resilient.

and not to mention it just sounds dumb and something a toddler would make up.
just like if people referred to their manual transmission cars as "stickies" or "clutchies"
or their surfboards as "wavies" or skateboards as "rollies"
or more appropriately, calling a geared bicycle a "gearie" rather than a 10-speed or whatever.

valid? of course.
dumb? yes.