My Head-Canon I just thought of within the last few days, so this is hot of the presses:
Running with the idea that the Enterprise-F had multiple crews and multiple Captains, as per what Terry Matalas has said (I don't remember where off-hand and not going to go fishing for it at 2:30 in the morning), I think Starfleet did this to keep the Enterprise crew from knee-capping Starfleet Officer's careers.
Take Riker, for instance. He stayed First Officer of the Enterprise-D and E for 15 years. If he'd accepted a promotion to Captain sooner (i.e. even before he joined the Enterprise), how many First Officers would've served under Picard? How many other careers would've been made because these up-and-coming officers got to be First Officer of the Flagship? But Riker stayed and stayed and stayed and locked others out of having that position. And why did he stay? In hopes that Picard would either retire, get promoted, or get killed, and they he'd become Captain. He wanted the Enterprise so badly, and made it so obvious, that Starfleet wasn't ever going to give it to him.
Then there's Picard. A Captain with decades of experience and unafraid to stand up to Admirals. If Starfleet had inexperienced Captains who were ambitious and wanted to become Admirals, they'd be far less likely to push back against those Admirals when or if they disagreed with them. By the end of his time as Captain, Picard had a ton more experience than a lot of the Admirals giving him orders. Starfleet probably wanted to avoid that with future Captains of the Enterprise. So, they didn't want experienced Captains, they didn't want to keep them there long, and they wanted Commanding Officers who were more on the same page with Starfleet Command. Shelby shot up through the ranks to the Admiralty, and someone like her probably saw the Enterprise-F as something could be a stepping stone for future Captains and Admirals.
In my head-canon, Shelby was in command of the Enterprise-F during the ceremony in Picard because as the E-F was being decommissioned, because the last Captain had been promoted to Admiral and the First Officer had probably been given command of some other prestigious ship after having cut their teeth on the E-F. Shelby loved that the E-F with was anthesis of the E-D and the E-E. As an Admiral, she probably helped to guide the Enterprise-F in the opposite direction throughout its lifetime...
... then during the Celebration she gets killed by the Borg and her Interconnected Fleet is assimilated. Her over-ambition and her pushing back against the philosophy of the previous Enterprises being her Achilles Heel.
So the Enterprise-G becomes the true successor to the Enterprise-D and E. The Enterprise-G with Seven's crew are the crew that helped the Enterprise-D and Picard's crew save the Federation from Vadic and the Borg Queen....
... which will make the Enterprise-F the black sheep of the Enterprises.
Now I'm going back to sleep. Or will try to. I don't think this was as effective as counting sheep. But, if I fall asleep, maybe I'll dream of electric sheep. Or at least see unicorns. Maybe not.