Maybe because this site is free to join.
I dont use dating sites for anything other than to find information on scammers so I may not the best one to comment but from what I have seen, and I have seen a lot of dating sites, the paid for sites generaly have a smarter type of scammer than the free ones, they need to be smarter or go to more effort to get a profile on a paid site so those that get past the initial barriers are usually the smarter ones, dont be lowered into a false sense of security on a paid for site, the scammers are still there
Thinking about free sites alone, there are some that are virtually scammer free and others where you need to wonder where the real people are, it really depends on the site's owners and their attitude and knowledge in regards to scams.
Free sites make their revenue from advertisements, the paying advertisers dont distinguish between a real person viewing their add or a scammer, the site owner gets paid all the same, removing scammers from a free dating site actually decreases the site owner's potential to earn add revenue.
Some of the better dating site owners actually do have a conscience and in return the word of mouth can help to increase the real members on their site and so increase their potential for more revenue but for the amount of work involved to make a site scammer free it actually makes better financial sense to simply have a second dating site and let the scammers run amok rather than taking the time needed to keep your site free of scammers.
Fortunately, some site owners do care and do have a clue about combatting scammers, some admitedly care but dont have a clue how to fix it while others dont care and let the scammer roam free.
The trick for dating site users is to know how to spot the scammers at an early stage and in time you will, if there are too many scammers for your liking, vote with your feet and move on to another dating site.