Liking the page would require effort from the user and most are reluctant to deviate from their current thought process.
Most people are on facebook to scroll down their news feed and maybe like a post or 2. There is no motivation for them to go to your page and just 'like' it, unless you have content that appeals to them.
People are bombarded with advertisement all day every day, they simply feel no obligation to help you unless you can provide them with something of value.
Think about from your own perspective, how you use something like facebook. Do you go and like random pages from people sending you unsolicited invite requests? Probably not, so why would anyone else do it.