I sort of did this, although not intentionally. Here's why-
Best friends for 20 years. Looooong history of me being the "supportive one" and helping my friend though various marriage crises, work crises, family crises etc etc I used to drop everything when she needed me, listened for hours on end about her husband's poor behaviour, travelled an hour or so to meet with her, listened to her job woes and gave advice etc
Then, when one of the few times I had a crisis we arranged a phone call (as we live about 2 hours apart) and she "forgot" the time I was meant to ring her and didnt answer. I was in tears by this point, I had been there for her whenever she needed me and the one fucking time I asked for support she "forgot".
Other stuff happened like she excluded me from a meet-up with mutual college friends on my birthday and lied to me about it but still I gave her the benefit of the doubt.
Then, a couple of years ago she had some serious health problems - I, again, was there for her. Texted her often offering support and got radio silence back. She never replied to me, never rang me back etc By this point I had had enough of being treated like shit and so I dropped the rope entirely.
Two years passed by and then I get a phone call from her telling me how she'd been having all these tests and was so worried about her health. By this point I simply didnt have it in me to care any more. I dont wish her ill and I hope she is ok, but after years and years of bending over backwards to support her and getting nothing back I simply couldn't do it any more. It was making me feel like I was being used.
I dont hate her or anything but frankly, I dont care any more about her health issues. Perhaps if she wanted support she could have just once in those two years considered my feelings for once. But she didnt, and so as far as I am concerned our friendship is done and she'll have to navigate her health issues alone I'm afraid. However, if you were on the outside looking in and didnt know all this, you would probably assume I am cold and heartless.
Please bear in mind that just because someone is experiencing health issues, it doesnt mean that their previous behaviour was always 100% kind or decent.
Sometimes there are genuine reasons why people withdraw.