LastPass password manager

Why is the LastPass Password Manager program not available for downloads in the iTunes or Apple store for use in Safari on the MacBook? Several other password manager programs are available to download as an app but not LastPass. Instead, I have to download the extension from their website, open it in applications and enable it in Safari Preferences. However, it can not be activated, not recognized, nor can it be found under Safari Preferences. Last Pass works as advertised on my PC browser by auto populating usernames and passwords. In order to use it on my MacBook, I have to copy and paste separately from the LastPass Vault each time. Again, how can I get LastPass to auto populate and be recognized as an extension in Safari on my MacBook? Thank you.