Why were they withdrawn after only 5 years?

Two separate sources explain the situation for the 2 different models；

for the Youngman trolleybuses, the 2012 and some of the 2013 batch were set aside in 2017 when the trolleybus network was reduced as a result of metro construction. However, when set aside, mandatory yearly checks were not performed and after missing 3 checks in a row, they were withdrawn.

The others, Yutong trolleybuses, were apparently bought in a contract with an extremely low price - perhaps up to 1/2 the expected price of such a trolleybus. Consequently, their quality was quite bad.