This kind of work is typically outsourced, since it's not a core competency for the company. So the company would be contracting some web development agency which builds a homepage and potentially also hosts it. There are contracts and specifications in place around what needs to get built. In the web development domain I don't think the outsourcing aspect is a big plus or minus on execution ability. There will be some good and some bad agencies around - and an internal team might not really be doing a better job.
Regarding performance: They mostly wouldn't even recognize. The work is presented with some fast connection and device, so it's not visible. And even if it would be, the people responsible for it (or even the leads of those companies or teams) are not that tech savy and will just accept it as the current state of the art.
There will be far bigger discussions around other things than performance. E.g. which images and fonts are to be used, how trademarks and the brand are represented, etc.
I used to work at an ad agency several years. We were locked into Wordpress or Drupal with Bootstrap and some base plugins for sliders as well as a ton of stuff for 'SEO' and tracking. The amount of time allotted to deliver the project was actually pretty small. You would get a mild scolding if you even bothered to look at performance. A lot of these things are a part of the theme/plugin out of the box and may not be optimized, but the images and the content was usually uploaded by an intern or whatever and they never bothered with image optimization.
we actually care about that, but our options are limited. of course, if the performance is heavily affected we can tell them to buzz off, but usually it's not a single tool that generates the problem, but the sum of all of them.
on the other hand, i'm aware that there's some value added by those tools.
- bad project management from the client (they often don't care about technical quality or rather can't evaluate it)
- bad project management from the web contractor (they often don't care about technical quality or rather can't evaluate it)
- the web agency has too many projects due and needs to deliver asap
- exhausted & mismanaged dev teams (+ freelancers) which are constantly working on short lived projects, which are a mess because nobody doesn't really care
Also I am amazed over and over again how a lot of managers (or people) will lie straight to your (or the clients) face if they can thereby save their ass.
One thing that wouldn't surprise me would be to see that the websites for some of the companies mentioned in the article are running on SharePoint. --If tuned properly, it can be quite fast, but like other solutions, it can also feel bloated and slow if it's not prioritized.