You're right, if we took this attitude in civil engineering or medical science then it'd be a problem, but hey, it's not those things, so why waste the time, money and effort that it would need?
You say "obviously not every web project is as important" as civil engineering, but I'd put it the other way "Almost every web project is not anywhere near as important" as civil engineering.
People build Ikea shelving units in their home all the time, without a civil engineer being involved.
Ikea shelves often break, and thus commonly need replacing every couple of years. This might end up with a higher total cost/kg/year for holding your stuff up in the air, compared to hand building your shelves out of oak or whatever.
Of course, many people move apartments each year anyway, and the old shelves will not fit in their new apartment. So it makes sense to use ikea shelves in this case. Unless of course, the handmade oak shelves were modular and could be easily reconfigured in a way that the pressed-fibre ikea shelves couldn't.
The real problem comes when your ikea shelves fall down, breaking all your stuff. In which case, you were an idiot for putting your important stuff on ikea shelves. In this scenario, you may wish to hunt down and disembowel the interior decorator who told you the ikea shelves would be fine.
So yeah, the right tool for the job. Who'd have thought it? ;)
Personally I won't be giving up my life as a designer of premium bespoke home storage solutions for a job on the checkout at ikea.
You say "obviously not every web project is as important" as civil engineering, but I'd put it the other way "Almost every web project is not anywhere near as important" as civil engineering.
People build Ikea shelving units in their home all the time, without a civil engineer being involved.