On ebookers, you can sort by price (Preis), by flight duration (Kürzeste Flugdauer), or by departure time (Abreisezeit).
The default is price, and naturally enough, these unattractive long layovers tend to be cheaper.
There will be no voucher for food or drinks. The reason such itineraries are cheaper is because of the inconvenience of long layovers. As such, the "cost" to you has been factored in already, and they won't provide anything further (if you have status with Air Berlin or Etihad you can use their lounges).
The fact is, though, that such itineraries may suit some people, who may have some business that they can attend to during the day on such a stopover, or who may be able to visit friends/family, etc.
I would encourage you to look into having a quick tour of Abu Dhabi, particularly if you have never been before.
As it happens, the only itinerary I can see on this route that involves a long stopover of 14h35 is, at least largely, a daytime stopover. EY403 from BKK arrives in AUH at 11:55. EY1401 leaves from AUH at 02:30. That is a nasty time to be leaving, and that is a long layover, but it is not an overnight stay. I don't think this would ever have been considered for an STPC for this very reason, even if it was the only valid option.
And just to let you know, I know of no airline that offers STPC on the cheapest economy fares. At best they would offer a package that you could pay extra for. You could still, perhaps, request a day room on further payment.