I think the problem for routes traveling between Tuen Mun <-> Kowloon East is that the non-peak hours may not have enough passengers to cover the cost.
Therefore, KMB may not be willing to extend the service hours of 62X.
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In my opinion, I do think Tuen Mun Town Centre should have direct bus service to East Kowloon.
If KMB insists 259D skipping Tuen Mun Town Centre, then I think KMB should consider whether it should reorganize the routes of 258D and 259D during non-peak hours,
e.g. 258D having similar routes with 960 in Tuen Mun...