The axles do have slip-joints on each end, so, they can compress/extend as the suspension travels. Seeing the boots expand a bit while tightening is normal.

Why his is ripping so quickly is a puzzler though. Just poor quality boots?

 

This probably won't help you right now, but maybe if you see a split forming on the next one, or any cracking rubber....

I had put in some cheap greasable NAPA ball joints which were fine for a few years, then the cheap rubber start cracking all over. Next time I put grease in, it starting coming out the cracks. Look at the right side and you'll see it oozing out.





Well, I didn't wanna replace ball joints and pay for an alignment again... so necessity being the mother of invention, my cheap azz thought about that tube of Permatex Black (oil resistant) RTV, that was drying up. I cleaned the rubber with brake clean, then applied a few coats, letting each coat dry (somewhat) in between. Amazing how strong the rubber is now. I put a heavy bead around the circumference where you saw the most cracking. The dried Permatex is way stronger than the original rubber. No more cracks or leaking years later.

 

Those CV boots look to me like they are being stretched more than normal. I don't have an explanation for that. Not using wheel spacers?
Take a look at high angle CV boots, they'll have more travel.

 

I’d say it has more to do with quality…..in my shop I’ve done my fair share of cv axles, the cheap ones from autozone, o Reilly’s etc usually tear within a year but they have 2 yr some 3yr warranties…..my drivers cv has been on my truck 8 months and it’s already torn the outside boot, ive put maybe 3k miles on that axle, but it was a cheap duralast autozone one