This is normal. Even with a lot more supports, a heavy walker can still make the floor bounce, and that will feel like trailer movement. TTs, for mobility, get lightweight construction.
This happens in the housing industry too. My brother bought a house built in the '80s in which the floor bounced. The floor was panels over widely spaced trusses, each section was like a drumhead. Next house he went back to the '50s for heavier construction, 12 inch joists on 16 inch centers, hardwood subfloor. No bounce.