Sliding door installation is a process that even some DIY aficionados might be able to handle, though pursuing that route is a risky proposition. For one thing, they likely have a limited background or do such work as a hobby. In other words, if something goes wrong, they likely aren’t offering a warranty to guarantee their work.
That’s not the case with professionals who install sliding doors all the time. They’re more than happy to put their name on such work because sliding door installation is likely just one of the areas of expertise these individuals possess.