I don't think it was so much the business practices, but the market that shifted - I think it was a viable business for most of the 90s - there were a lot of these shops, but most have disappeared. It made sense to build for a use case to save on parts, but now, the most basic PCs handle most computing tasks with ease.

Purchasing decisions in business and government were more ad-hoc - I can remember selling and servicing a small number of PCs to embassies, even federal government offices buying 1-5 units. Now they'd buy standard off the shelf boxes in huge quantities.

I just can't imagine now, a foreign embassy calling in to their local PC shop for service, and having a local 17 year old walk in to service a diplomat's PC.