I can understand your point. But Butter biscuits you prefer but someone may not like it, chocolate /cream biscuits u may like but some other person may not like it OR maybe the other person is suffering from some disease like say diabetes so he/she may not prefer cream biscuits or chocolate biscuits. Senior citizens dont eat butter biscuits, cream biscuits, chocolate biscuits, etc. Railway cannot give different type of biscuits to different persons as per their choice in a say 16 to 18 coach Rajdhani/Duronto/Shatabdi/Gatiman Exp whatever u consider. It will be too costly for IR if they have to give different biscuits to different persons as per passenger demands. So, a common biscuit which almost all age group can eat i.e. Marie biscuit which older passengers can eat and other age groups can also eat is given in trains.
You...
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cannot compare a bus with a train, bus has only say max 74 seats (correct me if i am wrong) whereas a train has 16 to 18 coaches and huge number of seats.

This is what i said but u didn't understand i think.
When passengers paying high their expectations can be high i agree, but their choices can be different. Now Railways cannot purchase biscuits according to your expectations na? For a 16 coach Rajdhani Exp, around 1100 passengers say + spare qty for 1 direction trip from HWH to NDLS.
If every passengers have expectations of different biscuits then please do Permutation and Combinations and you will get the total qty of biscuits of different variety railways has to purchase. Is that possible? Think...
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logically.
Not possible. So, when you travel in trains don't keep that expectations that you r paying high so you expect better variety of biscuit than Marie gold. This is not possible. Totally childish expectations. There will a 1 variety of uniform biscuit for all passengers in a train. Since Marie biscuit is eaten by all age groups be it Senior citizen, be it diabetic, be it children , be it other age groups. So, Marie biscuit is given in Rajdhani/Shatabdi/Duronto, etc.
30 seat in bus cannot be compared with say 1000-1200 seats in a train. Is it comparable???