This is normal. That depends on your settings and the sites you are submitting to. BMD doesn't support every site and customization, maybe you set the wrong category, Captcha solving service is down, proxys don't work for specific country, bookmarking site closed registration or is offline...etc.
There are many resons for a low success rate and in most cases BMD is not the reason for it. So i think it does a very good job. You need a big list of sites (scrape them with scrapebox) and you will get many links. I have 4500+ sites and on ca. 2000 i placed bookmarks with BMD successfully. It's more important to me to get 2000 links then to get a 90% success rate for 100 sites.
The only thing i don't like is the price for decaptcher service (4$/1000 Captcha's). Still cheaper than outsourcing but deathbycaptcha.com costs 1,39$/1000 Captchas and is not supported.