Why is the title to real property permanent whereas some intellectual property is limited in protection?

Because they arose in different historical periods. First, all western property law starts with feudalism. Under strict feudalism real property ownership did not exist; it was a grant from the lord (not God, the land lord) to his vassal for a certain period limited by time or certain events. Over the years, vassals kept pressuring for extension of these terms, first for life; then to the lives of their children, then their descendants (heirs); then to anyone they could sell it to and their heirs. As you can see this last is essentially what we now call "ownership."

In those days "intellectual property," (copyrights & inventions) didn't exist. Inventions & the contents of art or written works wasn't protected by law. They didn't need to be because before the invention of the printing press and mass industrial production, it was so hard and slow to duplicate written or artistic work (remember all those monks copying books) or machines that the originator could gain wealth directly from the sale and skillful reproduction of his own work.

Comes the printing press and later industrial revolution. Now, anyone could reproduce what some other creative person could invent. So the idea arose for the state to protect the creator's right to exploit his creation. Excellent example: US Constitution, article III, Sec 8, gives Congress the power "To promote the progress of Science and useful arts by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."

Intellectual property is now at the same middle stage where real property was; exclusive but for a limited time. Note that Congress keeps extending copyright protection: What was once for the author's life was extended for 75 years (to give benefits to their heirs) & now corporations get 95 years protection. We are getting to a point where copyright & patent protection may one day be permanent -- just like real estate.

intellectual propberty and private property are all invented things.

but its eareirs to permanently own an extendent thing in space than to claim ownership of an idea. there is nothign new under the sun.