The main point is that airplane design is a trade off, and airliners are very heavily focused on fuel economy while smaller private jets have other consideratio

The main point is that airplane design is a trade off, and airliners are very heavily focused on fuel economy while smaller private jets have other considerations. For fuel economy you want high bypass engines and those have a big diameter (hence why the 737 MAX had issues getting the larger engines to fit). All other design limitations are getting less relevant for airliners because airports by now are well equipped. All of this isn't really news, the industry has been moving in this direction for a long time.