I take your point, Joachim, and I've occasionally suffered the same frustration myself, but I believe the disadvantages of leaving all inactive accounts open indefinitely outweigh the one advantage that you mention. You can see one reason in Mr. Delcamp's announcement here
Another is that if we didn't do it, there would be many thousands of inactive accounts sitting there on the database and having an impact on the performance of the forum. Sometimes the server and forum software struggle to cope with the amount of activity and the size of the existing database. You may have noticed slowdowns and SQL error messages on the forum periodically, and you may also remember when the forum's inbuilt search engine had to be disabled altogether for quite some time and we had to rely on Google instead. Although it was eventually re-enabled, further limitations on searches may be needed if it starts struggling again. I haven't counted up any recent figures, but I see that when I replied to a similar query in 2014, I mentioned then that the latest purge of inactive accounts had removed nearly 5000 of just over 7000 accounts. That is a lot of dead weight slowing down the search engine. You'd perhaps be surprised how many people join up, post one or two messages, and then never post again. So when you balance all that against the occasional benefit of being able to look up earlier posts from an inactive member, unfortunately a tough judgement has to be made.
Even so, there is still a chance that you may be able to track down the introduction from an inactive member, if you really want to. You can try sorting the "Introduce Yourself" topics in ascending order by author, using the drop down menu at the bottom of the page, and then paging through the posts until you find the username you want. (To speed things up, you can use the arrow icon at the start of the page numbers to jump to a later page in the sort results). Even usernames that are no longer linked to accounts in the database will still be alphabetically sorted in this way. And if the introduction is old enough to have been archived, you can try the same thing in the Archives of Public Space and its subforums
section. Finally, if someone had an unusual username it can be worth searching on that, in case others have used it to address the member in their replies.
Classical Guitar Forum.
"Experience is something you don't get until just after you need it." - Steven Wright