It's technically not even about Bitcoin's security since most people don't care about that. In fact, it's mainly Bitcoin's network effect that makes it so desirable. If you look at what coins are being listed the first on exchanges, it's always Bitcoin. If you ask people in crypto if they accept Bitcoin, even when they are hardcore altcoiners, they'll do it.
By always being the first with everything, you position yourself stronger in the market year after year. Look at the volume of exchanges that are reputable, it's Bitcoin as single coin that generates most of the volume. XRP is truly a joke with just $20-$40 million in overall volume when you look at its market cap. Ethereum is doing better on that front but it still is no match.
With lightning faster and cheaper transactions can be tapped into already. I'm using it on a daily basis and thus far haven't had a single transaction fail. The only inconvenience I experienced thus far was that it took about 30 seconds for a ~$200 transfer to settle (likely related to routing) but it settled. The fee was a whopping 26 satoshis, which on lightning is a lot actually.
If I for a second worried about an altcoin that potentially could overtake Bitcoin in every aspect, I would be holding quite a chunk of it. I don't see it happen.