Oh great, this again!

'An earlier protocol called DNS over TLS was already available but since it runs on port 853 and “does not look like HTTPS”, network operators that dislike DoT can easily block it. Most corporate networks will in fact do this by default.'
Hence why DoH.

https://blog.powerdns.com/2019/02/07/the-big-dns-privacy-debate-at-fosdem/