They do have a website. I would assume the problem is that nobody can compete with Amazons delivery network (and Prime) on price.
For example, for online searches (in the UK), I try Amazon, Wordery, and Waterstones.com -- but usually Amazon first. If they don't have something or for some reason I feel I need to look elsewhere, I try the others.
Interestingly, for old or hard-to-find books, many people in the UK use BookDepository.com and AbeBooks -- guess what, both are owned by Amazon.
(I try to make up by visiting my local Waterstones regularly and more niche bookshops like Daunt when I can, but of course during the pandemic that's gone out of the window).