Different levels of credit and risk with each.
Poorer CC holders get the raw deal with basic cards and higer interest charges as they pose the most risk for not repaying the debt.
Platinum cards are for higher earners and will have larger limits and lower interest.
They increase limits and the like if you prove to be a good customer, ie repay in full and pay no interest. The provider won't be making any money off you so they increase limits hoping you'll borrow more and get hit with their charges.
My CC limit doubled in a year without me asking for or wanting it to.