Sounddrop is 'free'. Why would any free service want to promote your music?
The same goes for any other paid distribution service as well. These services charge literally a handful of dollars for every track. That's not even enough to buy anyone's time for an hour at minimum wage.
Promotion is a pay to play thing. If you expect someone else to do your promotion for you, you need to to pay up, fair and simple.
That said, promoting your music yourself isn't terribly hard. If your music is good, editors at top blogs want to listen to it.
Two key things are:
1. Relevance - Don't send an EDM track to a blog that covers indie artists. I help artists promote themselves and the number one complaint I get is that editors reject their tracks because it doesn't fit the blog's audience.
2. Your email - Too many artists just ramble on and on about their inspiration and their upbringing and blah blah. Take a leaf from salespeople' playbook - stick to a maximum of 3-4 sentences. Simply identify who you are, what your song is about, and link to the song + any other collateral
You of course need a list of blogs to contact (shameless plug, I put together a list here [mods, remove if necessary but I thought it was a good fit]: https://midination.com/blogs-submit-music/
). You need to get good at finding email addresses since not every blog identifies the editor's name or email. Your best bet is to use tools like Hunter.io or AnyMailFinder. Else, just send an email through their contact form (every blog has one) and ask for the editor's email (most will be happy to help)
Do the same for Facebook page owners, Spotify playlist creators, etc.
This is the only PROVEN way I know to promote your music for free - reaching out to editors and playlist/page owners.
For everything else, be prepared to pay