They aren't artists impressions - the CAD/CAM packages can all do very high quality renders in a variety of projections and then you just pull in the back ground and tweak the angles, can all done by engineers no artists required all done in the time taken to make cup of tea or make an RUKforums post
A good intro for fusion360 here:
https://www.youtube.com/watch?v=sejMq84YREs
As someone who's currently studying a field of design, and also has an active interest in CAD modelling.
Firstly I can assure creating the actual model takes far longer than 5 mins, however if you're talking in the time it takes to generate a render from the 3D model, depending on your hardware you are indeed correct.
Old Fashioned drawn artists impressions are still relevant though, particularly in the early days of design development as it's far easier and more flexible to put your thoughts to paper in a quick sketch than to go straight to 3D modelling. Everything from animated films, games and cars start off as a rough sketch before it becomes a 3D impression.
Saying that, I used to work for an architects firm and they still used old fashioned artists impressions for the final visualisations alongside 3D renders, both have their merits and one of the good things about old fashioned artists impressions is that you don't need a knowledge of 3D modelling or expensive software. Many Architects/designers themselves left university about 20 - 30 years ago, so are often more proficient with the traditional mediums than with CAD. Artists impressions still very much has it's place even if you don't see it in official publicity material anymore.
In fact in many architects offices you'll still see traditional desks and drawing boards.
In the field of design I'm studying, we're still encouraged to use traditional artistic mediums.