https://www.hltv.org/news/28902/esl-trims-down-pro-league-to-24-teams-reveals-preliminary-invite-list-and-format
Here's a TL;DR: https://www.reddit.com/r/GlobalOffensive/comments/etk3m5/thorin_will_no_longer_work_with_esl/ffgvwx6/
TLDR on the context from my limited knowledge:
ESL pro league cut in half from ~48 teams to 24 which removed teams that had earned spots in the league from previous seasons or were contracted to play in relegation matches very soon to compete for a spot
Having limited or no communication with said teams which mostly found out that they are cut from the league/relegated to MDL via Dekay's reporting - Reference HAVU: and Dekay's reporting:
Using the public space to announce "invited" teams which aren't necessarily signed to the league to gain leverage to sign others and/or use teams which might not even be involved in the end as advertisement
Those are the keys point I've gathered and there is plenty I don't remember right now and are in the fine print of their league contracts etc.
Not to mention as another comment said, Thorin in general has sympathised with ESL in a lot of respects and continually called them the best TO in CSGO up until now shows he is being honest in his actions.
Edit: More Dekay reference - https://www.dbltap.com/posts/sources-no-prospective-member-teams-signed-esl-pro-league-agreements-at-time-of-esl-announcement-01dzcga7xa12
ESL pro league cut in half from ~48 teams to 24 which removed teams that had earned spots in the league from previous seasons or were contracted to play in relegation matches very soon to compete for a spot
Having limited or no communication with said teams which mostly found out that they are cut from the league/relegated to MDL via Dekay's reporting - Reference HAVU: and Dekay's reporting:
Using the public space to announce "invited" teams which aren't necessarily signed to the league to gain leverage to sign others and/or use teams which might not even be involved in the end as advertisement
Those are the keys point I've gathered and there is plenty I don't remember right now and are in the fine print of their league contracts etc.
Not to mention as another comment said, Thorin in general has sympathised with ESL in a lot of respects and continually called them the best TO in CSGO up until now shows he is being honest in his actions.
Edit: More Dekay reference - https://www.dbltap.com/posts/sources-no-prospective-member-teams-signed-esl-pro-league-agreements-at-time-of-esl-announcement-01dzcga7xa12