They haven't timed this particularly well. I'd have thought the best time to release a YOI movie would be just after the Olympics, when even casual fans who don't usually watch anime are hyped about it.
I suppose this means we're never getting a season 2, which means we'll never find out about Nats, Euros, 4CC, Worlds in that universe's season....you know, like the half of the season that actually matters.
Sorry for the double post, but I feel it's best to reply directly than make an omnibus post, which could get unwieldy.
I won't repeat what iorii and JRH said, but will add:
YOI is a labor of love by two fs fans. The original series production involved Sayokan and Kubo travelling to rinks around the world to take pictures, commissioning program music, costumes, and choreography, as well as the normal activities for producing a new anime series. For a film you have to do the same, if you are going to keep it at the same level as the series, let alone surpass it. All of that takes time, especially if you are going to bring busy elite skaters into it. I imagine many of the people tied to fs, including skaters, choreographers, etc. had very limited time in the Olympic season and that includes the summer before, even if the production was at the point to make use of them. That’s beyond Sayo and Kubo being able to line up the main members of their anime production team who themselves are extremely busy. Not just because they are quality people in high demand, but because anime staff in general are overbooked. It’s a serious issue in the industry, not a MAPPA-only problem.
Moreover, Sayo and Kubo were not about to create a slapdash sequel to milk money from fans. Sayo especially is not the type of creator to create a show just for $$. She created the concept of YOI during a low period in her life when fs was one of her few joys and shopped it around without success until MAPPA took a chance on an original series. Original series are not common, because they are more of a financial risk. Although people expected critics and fans to pay attention since she is well a well-regarded creator, no one expected it to be a breakaway hit in Japan, let alone popular elsewhere. It didn’t need the Olympics to become the one of the top-selling anime since 2000. Now that Yuzuru and Shoma succeeded so well at the Olympics, they have raised the prestige of the sport in Japan, so I doubt that numerous YOI fans, who continue to snap up the mountain of merch aimed at them, are going to forget or ignore the show.
Re: the series focus on the GP series alone. From a storytelling perspective it made plenty of sense to follow the GP series to introduce viewers to fs by focusing most on the 6 who make it to the GPF and especially the process that gets one of them there. That competition made for a solid resting place for a short series like YOI. Perhaps if a 2-cour season had been greenlit (unlikely in the current state of the anime industry), the rest of the season might have been fit in, but honestly I like the tighter focus of the GP series as an intro to the YOI world.
At the moment we have no idea what will be covered in the film. It is possible they might cover the Nats alone to show Victor and Yuuri struggle with V’s comeback while coaching Yuuri and Y’s change of rink, or do that using 4CC/Euros, or do a prequel to flesh out Victor’s backstory. I doubt they try to fit the whole entire 2nd half of the season into a movie, unless they pretty much skip Nats, briefly show Euros and 4CC and focus most on Worlds.
As for season 2, I am not sure where you get the idea there will be none. If you look at other extremely popular anime series like Free!!, you will see that even multiple movies do not mean new series will not be made. I think whether one is made is up most to Sayokan and Kubo. Again, if they feel there is more story to tell and that she and Kubo can do it justice, then I suspect it will be made.