Maybe because the dromedary (single-humped camel from Arabia and Northern Africa) is more common – and therefore more recognisable – than the bactrian (double-humped camel from central Asia)?
The official names are also a bit confusing – Camelus dromedarius and Camelus bactrianus. And the dromedary is sometimes called an Arabian camel. There are three ‘true’ camels – the dromedary, the bactrian, the wild bactrian, but you can also use the word camel to informally refer to llama, the alpaca, the guanaco and the vicuña.
Camels are actually amazing – they can withstand heat and cold, carry extremely heavy loads, and go for almost a week without water. They can plough fields, their manure can be used to fertilise crops and to start fire. They produce wool, milk and meat. And they can provide transport.