Kohler sink, stains easily...poor materials or just dont make them like they used to?

I installed a Kohler double kitchen sink in my kitchen remodel 5 yrs ago. I thought this was a premium product....
It is a cast iron enamel sink
The issue is .... it seems to stain very easily. Any coffee , or tea spilled on it seems to stain quite easily and requires extra scrubbing to get it clean.
We will, only when stained, use BarKeepers Friend, it is verry mild and much easier on the surface than something like Ajax powder.
I recall having OLD sinks that seemed to be impervious to most stains and I believe that this is a case in which "they dont make them like they used to" applies.
I assume the surface is either slightly etched or now somewhat rough and takes staining easily.
The question is.... what can be done to either POLISH the surface or COAT the surface once bleached to make the surface RESIST future stains.
Any chemicals welcome...thanks for any suggestions

stains

The only way that normally happens is when the surface glaze has been scoured off the sink. Call Kohler and ask them at one time Kohler cast iron products had a 20 year guarantee. Yours may be after they cut it back to one year, but it doesn't hurt to ask.

Is there any way to put some kind of coating on the sink ?

Assuming Kohler thumbs their nose at me, what material can I use on it.
Assuming I get rid of the thing, what brand of sinks are better?

sink

Nothing, and a commercial refinishing company will cost more than a new sink, in most cases.