The problem is that your accounts with these businesses can accrue innate value over time. If you have spent 4 figures on buying video games on steam, and then want to dispute a fraudulent charge, access to all previously purchased items can be suddenly and permanently revoked. No to mention data like friends lists, game saves, etc.

Even worse, for XL companies who force one account across multiple products, the two things can be completely unrelated. If Google is refusing to RMA my pixel 7 phone which arrived defective, I can't issue a chargeback on that phone purchase because they'll remove my access to the last 10 years of family photos, my email, my domains, and my GCP servers.

Sure you could argue that this is the exact reason you should diversify these things across different companies, but in some cases the tight integration between these products is a compelling feature. The price for that feature shouldn't include removing consumer purchase protections.

This may be true for honest people, but I’ve been dealing with people recently abusing the chargeback system because they just don’t want to pay. (It’s mostly young users in Brazil)

Very frustrating as a seller.

In the case of companies like Steam the answer is: Because some products are not available elsewhere. So it's not that you want to do business with them but that not doing business with them also cuts you off from a large number of other companies. Similarily, if your water company overcharges you then you still want to be able to get water even if you need to charge back or take them to court over the dispute. In some way, Steam has taken over the role of infrastructure for Game delivery and I don't think its unreasonable to recognize that by applying different rules to them in the same way your local power and water companies get different rules from a mom&pop store.