Idera (the company that acquired Sencha) own Embarcadero, the company who publishes Delphi. There's a third-party product called uniGUI for building Web applications with Delphi that heavily leverages ExtJS at the front-end. I suspect this has something to do with it.

Oh actually bringing back Rapid Application Development for the web would be great.

A quick way to inherit a lot of engineers

I don't believe this is the reason. Apparently most of the existing team are going. Some key community members and developers' departures are already confirmed.

http://existdissolve.com/2017/09/a-fond-farewell-to-sencha/ https://mitchellsimoens.com/next-chapter-in-2017/ https://twitter.com/dongryphon/status/911278681611370496 https://twitter.com/AnimalNige/status/911152490380451840 https://twitter.com/evantrimboli/status/910988537763323904 https://twitter.com/elmasse/status/906243331541360640 https://twitter.com/LemmonsGrab/status/911703530716618752 https://www.glassdoor.com/Reviews/Employee-Review-Sencha-RVW...

But then they just fired all of them apparently. https://www.linkedin.com/feed/update/urn:li:activity:6316923...

IOW, business as usual for any Idera acquisition (see Delphi)

I suggest you do a quick linkedin search for engineers that work at Sencha. It will be very enlightening.