Why do some Muslims say that visiting grave can be considered as shirk?

is not shirk to visit a grave the shirk is to cry over the grave and also read Quran and ask the death people to help for something to Allah....you can go and say alfatiha but that is.. the problem is that some muslims are going to graves especially that from good ulemmahs or scholars and their visit become as a pilgrim and then ask for something, pray in the grave and cry and touch the grave and read Quran...that is pure idolatry.