An interesting piece by Sir David Beamish, a former Lords clerk, on the anomaly of by-elections for hereditary peers to be voting members of the House of Lords: Hereditary peers
Attempts to get rid of the by-elections and let the hereditary peers gradually die away have been blocked by members of the Lords putting forward amendments so that the bills run out of time. Of course, attempts at Lords reform by successive governments have also failed.
I may have unwittingly played a small part in setting up this system. In the late 1990s I was teaching a course with Lord Skidelsky who was then a Conservative front bencher. He asked me if I knew anything about the old system of Scottish representative (elected) peers and I recommended a book on the subject.