Why do HA fillers last less time in areas with more muscular movement?

I have HA lip fillers and was told they tend to last less on areas with a lot of muscular movement. However I've been wondering for a while if the muscular contraction actually makes your body metabolise it faster and breaks it down or only displaces the filler? Because I can't really imagine how talking, eating, etc would dissolve the HA as it feels pretty hard. Just asking this bcause it kind of makes me concious about doing a lot of gesticulation with my lips for fear it will go away faster