No this took them probably less than a year or so because as I told you in my other comment they've spent the past few years since Arma3's release making DLCs and content updates. You're just being a salty child who didn't do basic research on what you were buying as this reforger is aimed largely at mod makers to make mods ahead of time before Arma 4 is released in the next couple years.

just remember guys it took almost 8 years for BI to get an early access game not even completely released, and this is already worse than dayz was

This is literally the early stages of Arma 4 development man. The past few years since Arma 3's release was largely just releasing DLCs and experimenting with ideas and the devs slowly opening up more to the community to get a feel for things to include in Arma 4.

Arma Reforger is not even aimed towards the average Arma player as its intended audience is largely content creators and especially the mod making community. Its more or less a testbed for some groundbreaking features like in game comms, better movement, better mod implementation, newer graphics, etc. The mod implementation is a big one because until now the devs have been very standoffish when it comes to mods but with this it is them officially supporting mods wholeheartedly instead of giving just workshop support which is kind of janky.

This is not arma 4, They've been building an entire new engine and are putting out this "tech demo" as you call it for feedback.