Transaction fee and transaction speed are main problems of BTC if considering it as payment tool. Concerning security - BTC wallets are rather strong
I believe that bitcoin has a lot to raise, starting with transaction handling, is currency limited to about 3-4 transactions per second, and more than that will only cause the entire system to be flooded with users, but the problem applies to all cryptocurrency types, You do not see it in other currencies because only bitcoins are getting a lot of traffic.
Bitcoin continues to control the cryptocurrency market because it has become the first cryptocurrency, it has the greatest amount of support and has been shown to have a stable system for a long time.
Most altcoins come out in 2016+, even if they manage to get a lot of value, they still can not get past bitcoin because they do not have bitcoin support.