Reasons? I like mine. But I hadn't had one for 17 years, so....
The faucets with the separate sprayer are generally the lower end of the spectrum. The faucet itself is generally not very high above the sink rim either. The plastic sprayers also tend to drip a bit and the water runs down the outside of the hose into the cabinet below.
I guess I have adapted to having two sources of water in my sink. I pull out the sprayer when I wash by hand to spot rinse soap off certain pieces and lay it in one side of the sink while I rinse other pieces with the faucet in the other sink. Got a split sink. To have to pull the end out of the faucet part would mean pulling it out and pushing it back over and over again. There is one kind with a big spring that you remove from a slot that looks to be better, but I found the spring to be extremely inflexible. Telling me that the cheap ones are the kind I like has made me even less happy about finding what I want. Maybe I will have to buy a high class faucet to get the look I wand and then add a cheap sprayer separately or not have one at all, but the pull out kind look to me like they are made to break and very annoying to use. I was going to put a faucet over my stove to fill pots on the stove in the house I am completely redoing,, but I decided for the use I'd get it was too extravagant for the expense. You still have to carry the pan of water to a sink to pour out the water you poured in at the stove. Maybe I'll invent a pasta pot that attaches to a drain.