[edited to fix overly broad proclamations]
Not just YouTube! That ? in a URL often means “the rest of this is not essential”. You may need it for, say, keeping your browser aware that your shopping cart has 4 items in it, or for TicketBastard to know you are 8,762nd in the queue, but if you are sending an e-commerce site link to a friend as a gift idea in the middle of browsing? They don’t need any of that stuff. The ? usually signals the start of the spyware, on YT, Amazon, EBay, most e-commerce sites, you name it.