A large number of denominations do practice foot washing on a regular or occasional basis, including (to my certain knowledge) Catholic, Anglican and Mennonite, and I have heard of others. All of them have something in common.
In each case foot washing is treated as a symbol of how people should treat each other, not as a thing that has merit of itself.
This is because virtually all denominations (and virtually all Bible students) consider that Jesus is here treating foot washing symbolically. He is not laying down a pattern of literal action, but performing a lowly task - in which the other person is treated as higher status than yourself - to indicate that the disciples must be prepared to undertake lowly tasks and to treat others as higher status than yourself.
In this view, actual washing of feet has merit only in that it reminds the people involved of how they should be treating others. Anyone who physically washes another Christian's feet, but then goes on to treat them disrespectfully or as having lesser worth, has gained nothing from the exercise and is not fulfilling Jesus' intentions.
For those who hold this view (which is the vast majority of Christians) this approach is not treating Jesus' commands less seriously, but in fact treating them more seriously, as it gets to the heart of what Jesus requires from us.