My idea is definitely biased by the fact that I am a security engineer by trade. I believe a company is ultimately responsible for the security of their users, even if the threat is the users' own behavior. The company is the one able to afford a security department who is competent about the attacks their users are exposed to and able to mitigate them (to a certain extent), and that's why you enforce things.

Very often companies use "ease" or "users don't like" to justify the absence of security measures such as enforced 2fa. However, this is their choice, who prioritize not pissing off (potentially) a small % of users for the price of more security for all users (especially the less proficient ones). It is a business choice that they need to be accountable for. I also want to stress that despite being mostly useless, different compliance standards also require measures that protect users who use simple or repeated passwords. That's why complexity requirements are sometimes demanded, or also the trivial bruteforce protection with lockout period (for example, most gambling licenses require both of these, and companies who don't enforce them cannot operate in a certain market). Preventing credentials stuffing is no different and if we look at OWASP recommendation, it's clear that enforcing MFA is the way to go, even if maybe in a way that it does not trigger all the time, which would have worked in this case.

It’s up to each user to determine how securely they want to protect their data.

Hard disagree. The company, i.e. the data processor, is the only one who has the full understanding of the data (sensitivity, amount, etc.) and a security department. That's the entity who needs to understand what threat actors exist for the users and implement controls appropriately. Would you trust a bank that allowed you to login and make bank transfers using just a login/password with no requirements whatsoever on the password and no brute force prevention?