I am sure the remains of the trackwork were covered over as the section was a major loading point for BCT and Midland Red buses in routes B80 - B89. It would have been after March 1947 when the last trams, on the 32 Lodge Road route, ran. It seems that when the area was being pedestrianized the track were lifted and re-sited during the re-construction work. This was possible as the buses loaded elsewhere by this time.
It was a good gesture to the historic past of the old tramway system that once operated from that part of the city.
The other section of trackwork, from the old system, that still exists, is at Rednal. (Photos are here on BHF elsewhere).
I believe the section at Rednal was chosen as little roadworks were done in that particular spot unlike other areas of the city.
It was also a good choice. Most people were only familiar with the tram routes that ran where they lived or used when visiting relatives and friends. But Rednal, tram route 70, was familiar with a large percentage of Birmingham's citizens - and from neighbouring places - as it was the place where so many, over very many years, had gone for a great day out. I went there a quite a few times, but in my case it was more for the tram ride than scenery.