First, returns on online dating are typically abysmally low, for everyone. Online dating shouldn't be thought of as anything other than a novelty. I think I heard somewhere that being short counts against you online more than in real life because of how easy it is to dismiss someone just based on that number.

Second, as I suspected, you haven't actually asked many girls out (is the number around 2-4?) This is most of the reason you haven't had success.

Yes, being at a height disadvantage means that overall it will be harder to get dates that you find appealing. This fact is what you are noticing, not that you can't. You said it yourself, there are short men who can get dates they like. Good looks help, but not a requirement. What are they actually doing you're not? Do you actually have to be highly successful to appear so? No. Just looking highly presentable, fit, well dressed in ones style, and yes, confident (in your own way, not a particular type of cockiness), is enough. Even those things aren't really necessary, but they help. Then it's just a matter of actually asking women you are attracted to on dates, enough women until one says 'yes', which will happen eventually. The only real impediment is that you haven't committed yourself to dating and figuring out what works, which is a typical problem with various excuses.