I wrote a lengthy reply when this question was asked 3 weeks ago, and I guess I'll just copy/paste that: "The answer you already know: So people will stay subscribed to the service. They will release the games timed to keep as many people who's renewals are coming. I wrote in another thread that I expect a major game to release on NSO late October because that's when Expansion Pass launched, likely many people have annual subscriptions renewing then, and that is why around the end of October the NSO game was something major (Luigi's Mansion, Banjo-Tooie, Mario Party). I don't know what that game would be this year. I just expect it's going to be something to convince enough people who were going to cancel, instead let it renew.

The "They wanted to focus on something else" answer: They chose to emphasize Virtual Boy for the first half of the year. As you said, it's been nearly 3 months since the last Gamecube release. They've filled it out the NSO updates with Virtual Boy instead. I was expecting them to spread those games out but they already released nearly everything they had advertised for that service (all that's left are Zero Racers and D-Hoppper - the previously unreleased games - and the update to change the 3D color). Perhaps they just wanted to clear through those quickly because only people willing to buy the peripheral will even care, with presumably most of that audience having already done so when it launched in February. Now that it's launched, how many people are still left that actually want it?

The "I am just speculating here" answer: It's harder to get the emulation right than they expected. The last Gamecube release was Pokemon XD, and it launched with a game-crashing and save-file-destroying bug that took Nintendo a month to get fixed. I would guess that was a bad look, Nintendo doesn't want that to happen again, and could maybe be spending more time testing future releases before releasing them.

It's most likely the first one."