The plumbers used to carry them on their trucks because of what was available from the store to them. Either the chrome single or double -handle was about all their was unless, it was special ordered. Today without special ordering the big box stores has even the faucets made for big pots which is nice, pull out sprayers, brass, oil-rubbed bronze, brushed nickel, and if you are willing to pay you can even order a faucet with diamonds set into them.
Plumbers who work in areas where it is hard to get around might carry some basic plumbing supplies like faucets as a matter of convenience but they probably wouldn’t carry much of choice. Therefore, when you call a plumber to replace a faucet it might be wise to have one sitting there so it can be installed. Faucets that you buy from the Internet that are imported from other countries might have installation problems because they may not meet U. S. standards.