blockchain – How do cryptocurrency exchanges work with so many currencies at the same time?

To implement automated single currency deposits / withdrawals for a business, many currency-specific codes must be in place. For example, if I want to automate the sending and receiving of bitcoins – I would write an application around the bitcoin software – the bitcoin core. Obviously, there will be no similar node software for each piece, Ethereum said, would have a different kernel, if it had one (this is an example). Would you need to write a new application that would fit this kernel? Does this mean that big exchanges write new software that does the same job but for each piece? Where am I wrong here, or is the development of cryptocurrency really complicated?