If they have Lifejackets on boats, why not parachutes on airliners?

They also have life jackets on planes, but I understand what you mean in your question. Putting a life jacket on is much easier than wearing a parachute. They are smaller, easier to store, weigh less and are therefore a great deal cheaper. Wearing a parachute requires skill, knowing how and when to pull the chute, how and where to land without causing significant damage to yourself. It would be all but impossible to enable hundreds of unskilled people to jump in one go, and also a jet plane flies a lot faster than a propeller driven one. What would happen to the flight attendants and crew of the plane - where would it ditch? I can totally see why you asked the question, but to be honest I can't think of a single reason why an airline would want to, or even attempt to provide parachutes, I think the money would be better spent developing new fire proof fuels, installing bomb proof cargo containers and ensuring other safety measures are developed.

If a plane is going down it would be to hard to get 100 people to listen to direction on how to operate a parachute, get them lined up and out the door in time. Plus if you don't open the parachute at the right Altitude people could and would die.