These things were a consequence of accounting rules of the era... 8-year deprecation period for computers meant that an IBM PC bought in 1983 had to wait till 1991 before it could be written off - becoming useless long before, creating a market for those upgrade cards that kept it somewhat alive.

When deprecation period was changed for 5-year with possibility for 40% deprecation in the first year, this whole thing evaporated somewhere in 1990s.