Modern US Bisect Stamp First Day Covers

I've done a search engine search for articles on modern bisect FDC's but have found no online articles and very little info in general about this topic.

Though rare, I have seen a tiny handful (over the past several years) of bisect stamp FDC's being offered up at auction. But of these few, they are either not U.S. or if they are, they are all pre-1950 (that I have seen). It's not difficult to find a number of bisect covers up for auction on ebay, but U.S. modern bisect stamp FDC's are seemingly non-existent.

Can anyone tell me why?

Is there any online free articles available which discuss modern U.S. bisect stamp first day covers?

Thanks in advance for your help.

Modern us bisects are considered damaged stamps and invalid for postage thus they would not be serviced for FDC cancels????