If they weren't
first serialized or published in any of MAL's current whitelisted publishers (Cycomics, GANMA!, KakaoPage, Lezhin Comics Webtoon, Naver Webtoon) then that's probably the main reason why they were denied. It wouldn't matter if they're on other platforms too. 😔
Check:
Manga DB Guidelines
Usually when submissions are denied, you'll get a message from a mod as to why they denied a specific entry.
Example messages:
"Your submission for the manga: [Title] been denied by a moderator. Reason: Your submission was denied because it is a web-only series which was not exclusive to the whitelisted web platform when it was first released (the series is released simultaneously on at least [number] different web platforms). To help us focus on adding series from the whitelisted platforms, series that begin on multiple different platforms will be denied for now. This restriction will be removed in the future. Please see section I.2.8 of the Manga Database Guidelines for more information."
"Your submission for the manga: [Title] has been denied by a moderator. Reason: Your submission was denied because it is a web-only series from a web platform which is not whitelisted (Ridibooks). Please see section I.2.8 of the Manga Database Guidelines for more information"
It looks like Low Tide in Twilight was first serialized/published in Bomtoon while Nerd Project was first serialized/published in Ridibooks (Source: MangaUpdates & Anime-Planet, see links below).
See:
https://www.mangaupdates.com/series/f5t6dxm/nerd-project
https://www.mangaupdates.com/series/zn8uhqz/low-tide-in-twilight
Low Tide in Twilight and Nerd Project are both on Anilist and Anime-Planet. If you have accounts there, you can track them there in the meantime or in your MAL blog or profile page until MAL decides to add them to the DB.
https://anilist.co/manga/165673/Nerd-Project/
https://www.anime-planet.com/manga/nerd-project
https://anilist.co/manga/144209/Mulgaui-Bam/
https://www.anime-planet.com/manga/low-tide-in-twilight
You can check this thread
Manga DB - Recent Entry Merges/Removals/Denials for some brief explanation as to why entries were denied or deleted. I checked but I couldn't find Low Tide in Twilight and Nerd Project, though; they have yet to update it I suppose.
If you're curious about the metadata then you can check on DBSentinel:
https://sean.fish/dbsentinel/search?title=Low+Tide+in+Twilight&entry_type=manga&status=all&media_type=all&order_by=id&sort=desc&page=1&blur=on
https://sean.fish/dbsentinel/search?title=Nerd+Project&entry_type=manga&status=all&media_type=all&order_by=id&sort=desc&page=1&blur=on
I've also been waiting for Nerd Project here so I can track it. Haven't tried to submit it, though. Sad that it has been denied. Honestly, they should increase their whitelisted publishers since most manhwa are published first by Ridibooks, Mr. Blue and Bomtoon before being on Lezhin or other similar platforms. Maybe they can at least allow submissions from those three...