Why do so many airlines use junk jets?

I've noticed already that airlines are using junk airplanes that are unpopular with passengers and have high maintenance costs does anybody know why? Examples are the Boeing 707, IL-18, Il-62, etc.

It’s usually because they like them and want a different challenge.

Higher fuel and maint. costs , but MUCH lower lease costs. U can get more profit with some old planes than most modern ones. 

But sooner or later u have to change them, cause pax hates old planes (even if game states its brand new, most of them haz low or negative ors plane rates), and they are loud.

The lease costs are so cheap it is easy to make a quick profit. They are very challenging, though. For example they require a long take-off/landing roll that excludes many large airports. And as has been mentioned, after the game world matures, they become uncompetitive. 

I've noticed already that airlines are using junk airplanes that are unpopular with passengers and have high maintenance costs does anybody know why? Examples are the Boeing 707, IL-18, Il-62, etc.

Because it's the beginning of the world?

Though Otto offers low demand at first, there are tonnes of passenger who are still sitting at airport, waiting for any airline who can fly them to their destination: regardless of price, services, or quality of the aircraft.

And the first goal of any airline is to survive its first month by gaining cash as much as possible. Old aircraft with poor performance but cater many passengers and required low amount of installment were usually the best choice. Through times, they will get rid of these old junk (to be later used by newcomer as used aircrafts).

Not to mention that some old planes haz ~61% profit margins on some routes at 100% (default )ticket prices , and they can fly intl and very short dom. routes too. 

Meanwhile new ones had only 40-50% on the same routes.

If you mean otto, then those planes are available as new so there are no additional maintenance cost that ususually come with those jets. Also you can buy them at 1960 price tag with 2017 dollar.

Friends, i have started a poll in ''Suggestions and Ideas'' whether to restart Otto 2 or not. Please do vote

Otto 2 is a total failure. IL-18d cancer has spread all around Otto 2. Slot availability has fallen even below 10% in some airports (Beijing 3%) even within 2 weeks.
Raise your voice now. Please do vote and let others know u r opinions in ''Suggestions and Ideas''