Because the USP(T)O doesn't bother insisting on there being "no prior art"..before accepting patent applications and even awarding patents..
So the Corps with the biggest lawyers available file..
And if they do fall foul of "prior art" or are found to be infringing someone else's previously registered patents..they don't care..unless the other party has big lawyers and lots of money too..if not..they'll just wear them down with years of litigation..
USP(T)O..should be put down..for incompetence..or hung for aiding horse thievery and fraud..
I don't want ads in my books so I would not tolerate ads in my digital books, especially if I paid money for them. I find that ebook distributers already push the creepy line on tracking my personal reading habits so 3rd party ads doing the same would be over the top.
As a webmaster I rarely buy online anyway simply because I avoid ads and can easily spot them.