It's a customer's decision, not a developer's one. A one liner like the one in the post should be added at zero cost by any developer, but more important optimizations compete with the budget of the features that sell the product of the customer. In my experience customers want features first, optimizations last and only if the unoptimized app/site runs too slow on their devices. And developers don't like to work for free.
Even if the customer doesn't demand it, you should have your own standards for quality and performance and never compromise on them when it comes to your deliverables.
You're actually harming your business if you choose to do shitty work for small bucks and good work for big bucks. If you take your standards very seriously it improves the capabilities of your team and let's you take on more lucrative contracts.
> And developers don't like to work for free.
Oddly enough, the highest earning developers I know don't think like that.
I understand your feelings but I don't think they match the reality of many places around the world.
Maybe those developers earn so much that they can provide quality even if their customers don't explicitly demand it. But we can look at it in another way: their customer pay so much because they also pay for that quality and take it for granted. Deliver to them an unpolished product (in any way) and somebody else will code the next one.
Unfortunately not all customers are like that. Many of them fight for every single dollar/euro/whatever. They know they are compromising on quality and accept the tradeoff. After all, it's their privilege to decide the limits of their budget and maybe there is nothing they can do about it. The developer must accept it too, get the job done as quickly as possible and take another job. Or do very few and very long high quality jobs at unbearable costs and end up bankrupt quickly (and possibly piss off the customer because you're taking so long to deliver.)
Btw: customers give constraints also on time. There is no time to provide much quality when they want a feature delivered in a couple of days on a system you never saw before. It happened to me a few weeks ago. I made it but I could have done it better if I had at least one week? Sure. Would they pay me twice as much? Nope.
