Why does tea/coffee on trains taste yucky ?

Inspite of travelling weekly on trains, I avoid the tea/coffee sold aboard the train because
it has absolutely no resemblance in taste to what I know as tea or coffee. So, on my way to Kerala, I get tea from a restaurant on Kottayam station where the train stops for 5 minutes.
And on my way back to Chennai, I have tea at the Rathna Cafe restaurant (a little too thick
for my taste, but still OK) in Chennai Central station.

The weekend before last, I was on the train to Kerala, which was approaching Kottayam
station and I was near the door of the compartment planning to detrain and get myself a
cup of tea. A Railway policeman walks past me immediately followed by a vendor selling tea/coffee.

They stop at the vestibule area which connects 2 compartments and discuss something.
The vendor complains about how dull business is and how he is finding it tough to make
ends meet. The cop dismisses this line and replies that he believes business is good.

I know by now what the whole drama is about. The vendor must be unlicensed & the cop
is taking advantage of this by demanding a hefty bribe. The vendor is trying to negotiate
on the amount by saying that business is dull, while the cop rebuts that argument so that
his cut is not reduced.

As I stand there, the vendor takes some money and hands it over to the cop, who pockets
it without even worrying about the fact that I am a witness to his taking a bribe. Then the
cop moves on to the next compartment, while the vendor returns back, maybe mentally
cursing the cop for taking a share of his hard-earned money.

Since these vendors have to line the pockets of the cops, they would need to account for
this revenue loss somewhere or the other and what better way than to shortchange their customers, by serving watered down tea / coffee. No wonder the tea/coffee tastes so bad.