Why would people buy bitcoin these days if its too expensive? I'm curious on why would bitcoin rise in the near future since its not affordable anymore. It's actually but for wealthy people only. How could it even reach mass adoption because of its extreme price? 

It seems reasonable that people will switch to alt-coins because of their lower prices hence that would cause bitcoin to loose its value over time since people will start to sell it.. 

How can people/experts make claims that we could see bitcoin over 100k etc. It's total nonsense or am I missing something?
What you are probably missing is the fact that you can buy partial bitcoins, you don't have to purchase a whole bitcoin at once. You could buy a small bit of bitcoin for $20 if you wanted, it can be an affordable investment for anyone.