Why don't frequently used websites with average - boring designs update their UI / UX?

Just trying to understand; Why don't frequently used stress on updating their UI / UX to the newer era? For example IMDB is still stuck in 2005, [https://medium.muz.li/imdb-redesign-concepts-39a832b7867d](whereas people've had their go at revamping it.)

I understand it takes a while to research and money to implement new designs on complicated websites, but wouldn't it market itself better once it has a newer look, making it easier for people to browse the site?

IMDB is only one example. Ebay is another (slowly updating but I feel they're terrified of updating it still), Amazon is another, etc.

Just trying to understand why this is the case.

Great design resource

100 Things Every Designer Needs to Know About People (Voices That Matter) Submitted March 15, 2018 at 07:28AM by thedefaltcondition http://ift.tt/2FWp5sM