why?
Longer travel times, competition from London Underground network.
Brill Tramway
On 1 July 1933, the Metropolitan Railway, along with London's other underground railways, aside from the short Waterloo & City Railway, was taken into public ownership as part of the newly formed London Passenger Transport Board (LPTB). Thus, despite Brill and Verney Junction being and over two hours' travel from the City of London, the Oxford & Aylesbury Tramroad and the former Aylesbury and Buckingham Railway became parts of the London Underground network. The locomotives and carriages were repainted with London Transport's Johnston Sans emblem.

By this time, the route from Quainton Road to Brill was in severe decline. Competition from the newer lines and from improving road haulage had drawn away much of the tramway's custom, and the trains would often run without a single passenger. The A Class locomotives were now 70 years old, and the track itself was poorly maintained. Trains, once again, were regularly derailing on the line.
which country does quainton road railway station belong to? England which two places does it connect? Aylesbury, Buckingham Railway was it ever expanded? Yes - to extend the route to Brill when was it opened? 1872 who did so? UNANSWERABLE when did they close it? 1935
wiki:4165651
Brill Tramway [SEP] London Transport
On 1 July 1933, the Metropolitan Railway, along with London's other underground railways, aside from the short Waterloo & City Railway, was taken into public ownership as part of the newly formed London Passenger Transport Board (LPTB). Thus, despite Brill and Verney Junction being and over two hours' travel from the City of London, the Oxford & Aylesbury Tramroad and the former Aylesbury and Buckingham Railway became parts of the London Underground network. The locomotives and carriages were repainted with London Transport's Johnston Sans emblem. By this time, the route from Quainton Road to Brill was in severe decline. Competition from the newer lines and from improving road haulage had drawn away much of the tramway's custom, and the trains would often run without a single passenger.