Mobile menu only?

I think it comes down to functionality rather than aesthetics, mobile users are very used to to seeing a hamburger menu, desktop users are not and a great proportion of them (my 91 year old brother-in-law included) would not know the meaning of it.

Some folks really like the minimalist, uncluttered approach to web design.  I can't say that's a bad thing.  As long as the site communicates its message clearly, there's nothing wrong with minimalism.

All the browsers and apps we use today have the ubiquitous "hamburger" menus.  So it's no great stretch to see them utilized on desktop sites.  If that's what the client wants, go ahead and use it.

Nancy

This is likely a decision made by the developer in pursuit of a visually pleasing layout rather than a user friendly layout. I cant say l mind either way, everyone these days knows what the hamburger icon is. I've considered using just the burger which evokes an off canvas navigation before, so its not a new trend its been about for years.

Also its safe to say the majority of website layouts are similar these days because we have discovered the optimum way of laying out a website with the techniques availabe today so any slight variation away from that has to be positive to some extent.

It's possible, though not very likely, that an overwhelming proportion of visitors for the site are coming from mobile devices and the client(s) felt there was no need for a desktop-friendly menu and asked to annoy desktop users by forcing them to click to open a basic menu system.

I think it's more likely the designer either doesn't know how to create a desktop-friendly menu that disappears correctly in mobile (maybe due to a limited knowledge of whatever framework they're using) or they just didn't want to deal with it and simply left it off (the "good enough" attitude).

All depends on the user base. It is no use just having a 'hamburger' menu if the user has never used a mobile device's browser, as they will have no idea what the 'hamburger' icon is for.

Then there is the lack of flexibility that comes with having a 'one size fits all' menu set-up. Users expect 'cut-down' features on mobile devices, but do still expect the full 'bells and whistles' to be available on desktops or similar devices.