I've definitely noticed the trend towards making MMOs mostly solo-able, and personally I am not against it. I like to have total control over my social experiences in MMO games, and do not want to be 'forced' into grouping up. I always want it to be optional.

https://www.mmorpg.com/features/why-do-you-think-old-school-mmo-design-is-so-alluring-to-fans-of-the-genre-even-today-2000126990

Why Do You Think Old-School MMO Design Is So Alluring To Fans Of The Genre Even Today? | MMORPG.com

Many MMOs come out of the woodwork professing to bring back the feel of old-school MMOs. From the recent release of Ember's Adrift, to Pantheon which takes cues from the early days of the MMORPG genre, this is an alluring concept to prospective players.What about it is so alluring?

MMORPG.com
@ghique Guild Wars 2 has some good single player content, and its "living world" events are a great way to organically group up. Just wish I could collect what I need for legendary gear without other people.