While cash games will always be a primary focal point for poker, multi-table tournaments are now a much favored format both for live and online poker players. In particular, players love the low buy-in, big field events that afford opportunities to win huge returns on relatively small investments.
You'll never win 100 or 500 or even 1,000 times your buy-in during a cash game session (unless the session lasts for a long time). But it's often at least a possibility in large field MTTs to enjoy a huge windfall-like ROI, which makes them all the more attractive to many.