This is a myth.
Firstly, corporations don't have fiduciary duties. Corporate officers, directors, and employees who act on behalf of the corporation, have fiduciary duties.
And those duties (in the US, as far as I understand it) amount to putting the company's interests above their own and making responsible, informed decisions. That doesn't mean always putting the interests of the shareholders before the customers. Its a judgement left to the people acting on behalf of the corporation - as long as they can show that their decisions are reasonable and not made out of self-interest.
Edit to add: This is also the basis for Corporate [Social | Environmental] Responsibility. People with fiduciary duties can reasonably decide that it is in the interest of a corporation for it to behave in certain ways within some wider context, even when that behaviour is not directly profit- or advantage-seeking.
> "There had been a lot of such rot let loose in print and talk just about that time, and the excellent woman, living right in the rush of all that humbug, got carried off her feet. She talked about 'weaning those ignorant millions from their horrid ways', till, upon my word, she made me quite uncomfortable. I ventured to hint that the Company was run for profit."
Lemon prices down this week? Quick! Stop manufacturing spoons! Buy lemon farms!
That’s obviously not true in the short or the long terms.
https://www.fudzilla.com/news/mobile/47872-cook-blames-users...
The current debate is thus over whether or not customer disgust with their declining ability to repair and upgrade their devices, and resultant lost sales, will do more harm to shareholder profits than lost sales due to people extending the lifetime of their devices by easily replacing batteries etc.