All of the above, plus attracting new users.

Comparatively, Twitter doesn't have the same user base as Instagram, Facebook, or WhatsApp, and I think that extending the character limit is a way of making Twitter more accessible for first-time users.

It's also designed to bring more brands to Twitter. Right now it's extremely difficult to promote your brand/business, include a photo, @ mention someone, and include a hashtag. An extended character limit solves all of these problems, making it a more attractive platform for advertising than ever before.

Having more text means more text to mine which would be something of a paid service. I can imagine a couple of ways, but imagine a real time feed of all long text "posts" which mention your brand, product, company.

Just what the world needs: more traps.

They don't have traction amongst normal humans.