50% of heterosexual couples meeting online is not the same as 50% of customers of dating sites entering a relationship.
It could be the case that say, only 10% of dating site customers end up in a relationship, and this 10% amounts to 50% of the total couples, and the math would work out.
E.g.: suppose the total population is 1000 people, 500 of which are on a dating site, and the total number of couples is 20, 10 of which were formed via the dating site and 10 of which were formed by other means, and 960 people are out of luck.
It could be the case that say, only 10% of dating site customers end up in a relationship, and this 10% amounts to 50% of the total couples, and the math would work out.
E.g.: suppose the total population is 1000 people, 500 of which are on a dating site, and the total number of couples is 20, 10 of which were formed via the dating site and 10 of which were formed by other means, and 960 people are out of luck.