reasons most gTLD-s will fail:
1) high prices for premium words and terms for some of the extensions...if you want wide adoption you can not price gouge like an aged .com...nobody will pay $xxxx for a "premium" .top or whatever...
2) low prices...will be swept up by domain investors and spammers...
https://www.spamhaus.org/statistics/tlds/
3) spam filters...mail from new gTLDs mostly gets blocked...there is a very widely accepted practice of blocking the new extensions because there are so few end users, but so many spammers...if end users can not send emails, this will cripple the extension and its adoption by a wider market...
4) most end users do not know about them...and there are so many of them <---bigger problem because: confusion... .com is easier to remember than .accountant for example...now they not only have to remember your company name but also your long ass extension...
5) ccTLDs are still abundant and better known than gTLDs