This is a philosophical difference, in a way - running an asset-light business vs an asset-heavy business. Hotels have mostly moved towards not owning their properties, for example.

Increasingly, many new orders of aircraft are leases. However, they are not usually leased directly from the manufacturer. The airplane is usually owned by a holding company ("trust"), and tranches of the trust are sold to investors - somewhat similar to a mortgage bond.

The benefits of this is that investors from all over the world can invest directly into the airplane, then lease it to the airline. The plane itself is the collateral, and international treaties make it easy for investors to retrieve the plane if the airline isn't making its lease payments. They could then choose to lease the plane to someone else, sell it to someone else, or to scrap it for parts and materials.

What are the benefits for airlines? Typically, if things go south, they don't owe anything beyond giving the aircraft back. Also, given that many US airlines have gone through Chapter 11 recently, I'd assume they wouldn't get great interest rates if they actually want to buy the plane - it's likely cheaper for them to lease through an EETC. For example, American Airlines issued a bunch of EETC's the past few years.

It's a fairly niche subject, so the wiki page isn't too great, but here it is: https://en.wikipedia.org/wiki/Equipment_trust_certificate

Most aircraft of that size are leased new - and then re-leased or sold to budget carriers.[1]

New models come out and the airline may want to switch/upgrade, and it's a lot of capital tied up in one aircraft if they were to purchase them outright.

[1] https://aviation.stackexchange.com/a/2374/2294

Depends on the airline. Most Middle Eastern airlines, for example, own the aircrafts they operate though a small number were indeed leased.

A brand new A380 lists for $300 million dollars so not all airlines have the cash to pay for them upfront, enter leasing companies who put down the capital and rent the planes out to interested airlines. Normally when the lease expires it is off to another renter at a marked.down price, however in case of the 380 this may be a bit difficult since only a few airlines have enough volume out of hubs to fill the plane, and chances are they already have more aircrafts than necessary.

I don’t have a source to back this up, but I’d say 99% of all commercial jets are “leased”. The question is who holds the lease. I don’t believe it’s usually the manufacturer, far far more often it’s a “holding company” that’s associated with the airline. There’s extensive articles on the web that go in depth about why airlines don’t directly own their planes and rather lease from a holding company, but Tl;dr it’s mostly due to bankruptcy and tax reasons.

They are not leased by the manufacturers but by aircraft leasing companies like AerCap and GECAS.