2001 escape cv joints

I have a 2001 Ford Escape. There is about 47,000 miles on it and so far the CV joints ( trans axle???) has been replaced 3 times and seems to be out again. What causes this to happen and should the repair techs look for that
problem and replace it also???
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hungry to replace just the boot. So....they replace the whole axle....Also, some of the boots are just plain junk and dont last. Just my guess....I really dont know anything about the "Escape". Who is doing the repairs? The dealer or not?
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