They did displace/lend vocabulary to Romance languages. Every single Romance language has a long list of words of Germanic origin. For instance, in French,

guerre "war" ( < Old French guerre < Frankish *werra < Germanic *werso, cf Old High German werra "strife, quarrel")

And it happened less in Iberia, Gallia, and Italia because those places were heavily Romanized and had a Latin (and often Greek) presence. Places like the Rhineland and England were not heavily Romanized, or their Roman presence/identity did not persist long after the end of antiquity, and so they are more heavily Germanic and less Romance than French, Spanish, Italian, Romanian, etc.