I personally feel they DO that because it's easier to SHUN shomeone that is actually 'marked' or officially DF'd/DA'd - then for the inactive person (who is shunning) to LOOK in a mirror and admit that they themselves are just as f*cked up as the next person!
I actually work with 2 fleshly sisters who are and have been inactive for YEARS!!! These woman are both baptized, and both were well liked in the org, but chose to fall away and live their lives - which is fine. Both have dated, shacked up with, and formally MARRIED non-JWs...all public knowledge of their JW families AND also an elder and his pioneer wife who are VERY close to this entire family. Nobody shuns these women when they are are out and about showing off their husbands and haven't set foot in a Khall for years....the elder/pioneer wife have dinner parties and OPENLY celebrate anniversaries/dinners/and births WITH these baptized inactive sisters, and yet I am DF'd and spoke in passing to BOTH of these 'sisters' at work and both of them acted 'put off' by our conversation!!!! I didn't talk about Biblical things, I didn't talk about what I went through, and I didn't even go into Khall 'talk'...it was simple Hi How are you doing? type of thing. Now when I see them, they shuttle past me barely lifting their heads to say a WORD - and I find it ironic purely because these women are no better then I am. Only difference is that I was woman enough to stand up and take what was dealt to me....