"Table Stakes" rule in a B&M

[TexasBassDude]

This has happened to me the past couple of times that I have played live and I was wondering what the reason is:

Whenever I get up in chips, I want to cash out for some of them, but the dealer and the players at the table won't let me take just a portion of my chips off of the table, claiming a "table stakes" rule. What in the world is this rule and why is it called "table stakes"? Thanks in advance.