At the height of early computing there were relays (Turing-Welchman Bombe) competing with vacuum-tubes (Manchester Mk1 etc), and all had MTBF times measured in

At the height of early computing there were relays (Turing-Welchman Bombe) competing with vacuum-tubes (Manchester Mk1 etc), and all had MTBF times measured in hours. Constant replacement of valves and relays was a full time job. Why didn't magamps replace them? I don't think it was necessarily the efficiency, but the problem of doing logic using AC signals. Any EE's have thoughts on this?