Bitcoin launched cryptocurrency, and is the pioneer of all the coins we know and love so much now. It undergoes halving every 210.000 blocks (about 4 years) to control inflation, by increasing scarcity, which also has a positive effect on it price. Its last halving was this year (2020) and it had gone up by $3,000 since halving.
Bitcoin uses Proof-of-Work consensus, thus its mineable and can be mined for passive income. It can also be used to make payments to anyone, anywhere in the world. It is one of the worlds most popular cryptocurrencies, highly supported by pretty much every Cryptocurrency Exchange and wallet in the world.
Finally there isn't much being built on Bitcoin, rather we see a lot of forks, with the forked projects claiming to make a better coin out of it. Bitcoin would always be relevant being the first cryptocurrency, but that might just be the only reason keeping it among the top coins in the next few years.