I'm a bit late here, but better late than never! Bitcoin is a network, and therefore a lot of its value comes from its user base. Being the most valuable gives it the most attention, which gives it a big user base (at least as far as people who have heard of it).
That's also one of the biggest bull arguments for STEEM - it has the biggest active user base of any blockchain or cryptocurrency and by those metrics it is quite undervalued. The site https://blocktivity.info shows this well.
In any case, welcome to Steem - great to have you on board!
Thanks @yabapmatt! Indeed that was much of my argument, and I agree it could be a valid argument for Steem as well! It's certainly exciting to see a blockchain based app that seems to have vibrant, real world usage.
Beyond just users, Bitcoin has also had years of folks trying to break it, and it's security and incentive structure have been stressed more than any other. That it continues to operate well makes it more likely it will continue to operate well.