Timo could you please list some (let's say 3-4) examples where you think they ought to have mentioned/used the yacht?
"Samaritan Snare" involves a long trip that Picard performs for what he considers secretive, personal reasons - a good time to travel in comfort, on resources not needed by anybody else. The lack of a Yacht there seems to rule out its role as a private pleasure vessel. "Rascals" supports that view, again depicting a holiday trip; the conference in "Timescape" is only marginally less private an excuse. And it's not as if Picard used the craft for "Captain's Holiday", either - although everybody may have agreed that it was important to have him stuck on Risa, rather than free to travel and perhaps rejoin the crew before he had gotten sufficiently relaxed.
It might be the craft lacks warp engines and is just a glorified elevator for arriving on planets in style. (Why such a thing would be called a "yacht" evades me, though.) But "The Host" is an example of the Yacht not being a craft for ferrying dignitaries over short distances, either, or it would have been used by Odan there.
Also, "Q Who?" involves Q kidnapping Picard to a standard shuttlecraft. Why not the Yacht, all things considered? And "Final Mission" is unexplainable in its use of a non-Starfleet shuttlecraft to begin with, but that's a somewhat different issue.
It might be that the E-D did possess some sort of a utility craft for a mission type that never was witnessed in the show. But we saw pleasure yachting of various sorts, and that wasn't it. We saw infiltration missions, and that wasn't it. We saw flying through dangerous environments, and that wasn't it. About the only thing we missed was the ferrying of large numbers of troops (perhaps the Yacht performed an offscreen role of that sort in "Descent"?), or perhaps the establishing of a research or diplomacy outpost. The thing might
be a flying barracks (the shape would certainly cater for it) - but why call it a "yacht", then?