When watching the first part of trailer I was like : damn it's only Build, Ex-Aid and Ghost + suits.
Almost cried of joy at the end really. that's awesome.
So hyped right now

Would have been great if the rest of the phase 2 crew showed up but hey, so glad for this.

So happy Kouta's in the flesh this time, and not archive audio. I was shocked they got Gentaro's actor back, as he's a big actor now.

I'm shocked and overjoyed to see this turn of events. I was convinced we'd never see Gentarou again given his agency refusing to let him do more toku work.

Plus getting not just Eiji back but Ankh, too? I'm more than sold.

It definitely shows that they want this to be the most loved movie taisen of all time.

HOLY SHIT IT'S KOTA, GENTARO, EIJI AND ANKH?! SOLD.

Although it's rather weird Wizard and Drive aren't around. Maybe most of the money is used to hire Gentaro's actor.

Kamen Rider Build Detail of Heroes Full Scans:

Probably.
From the looks of it though it seems mostly because of schedule reasons for Wizard, Drive, and W. Kiriyama/Shotaro apparently has been busy filming a 25 ep action drama of sorts as one of the main cast, Suda/Philip is always busy filming a bunch of TV dramas or movies, Shiraishi/Haruto seems to have been busy doing bunch of streaming service exclusive shows mainly for Netflix and Amazon Prime, and Takeuchi seems like he too was busy filming TV dramas.

That can happen at times. It was the same reason Sano didn't come back for Dr Pac-man last year.

We did get to see Takeuchi and Shiraishi last year so I think it is fine if we don't get them for this new movie. Would have been great but they got people we thought was difficult such as Fukushi of all people so kudos to Toei's casting department for pulling this off.