People who say that Bitcoin is outdated are just repeating the words of altcoin marketers who make those claims in order to promote their own coin. They are making promises of millions of transactions per second, claim to be "blockchain 3.0" and promise to change the whole world, and in contrast describe Bitcoin as slow, old and inefficient. But anyone who understands the technology behind cryptocurrency sees that those altcoins are nothing more than vaporware, at best they have barely stable testnet without any features that were claimed, but most projects don't even have that. They're also extremely centralized and some projects have just 20-30 nodes in their network - these systems just can't be viewed as cryptocurrency. Bitcoin on the other hand is doing extremely well, it has survived many attacks and continues to get upgrades and has very realistic goals. So, to answer your question, many investors trust in Bitcoin's technology over altcoins. This created a reputation of stable and reliable coin, something that can't be said about altcoins.