I've been using PC's since 1981 and still find this type of software very unintuitive and "cranky" to use (and I've really persevered). The "search" function remains a mystery to me as it does to many members (judging from the lists of search terms that have been used)
Before we decided on SMF to house the forum we looked at a lot of others. I used to use IRC in the early '90s, when the internet was something most hadn't even heard of and that was a difficult way to do things. SMF has remained in vogue across the world for a number of reasons, It's easy to use once you've been doing it for a while, it allows for precise categorisation, it's extremely flexible and it can accept plug-ins and extensions, none of which Facebook can. However, the main reason is it's far more secure than Facebook, and with Facebook's acquisition of the infamously insecure WhatsApp you can expect a lot more problems with the already leaky Facebook.
Facebook, Twitter
et. al. are all commercial entities, that want to separate you from your money in as many ways as possible. We only have a few ads on here to cover hosting and we don't make a penny from it ourselves, so we have no axe to grind and can afford to allow members who reach a certain posting total to enjoy it without the ads.
You're right about the search function - sort of. There's trick to using it that isn't that well known. First off, it's pretty stupid, so don't expect the smooth correction algorithms like Google's. You do need to be very precise in spelling terms. Secondly, however, it will only search the section you're actually in at the time you invoke the search. The trick is to force the home or main page display and then enter the search parameters.
But, overall, we believe this offers a secure forum with the best mix of functionality and organisation for the cost (it's free:-).