Yes, traditional publishers do marketing, but the extent to which they do marketing varies from publisher to publisher. Some traditional publishers do very little marketing, while others do a moderate amount, and still others do a great deal of marketing. There is no one-size-fits-all answer to this question.
That said, it's important to keep in mind that the marketing efforts of traditional publishers are generally focused on the books they publish, rather than on the authors themselves. So while traditional publishers may do some marketing to help sell your book, they are not likely to do much to help you build your platform or reach new readers. If you're looking for help with marketing yourself and your work, you'll probably need to do that yourself, or hire someone to do it for you.
