It makes Americans products cheaper to buy, which in turn boost our economy. We sell more than with a strong dollar.
Or as https://edis.ifas.ufl.edu/publication/FE546# puts it:
A weak US dollar increases the demand for exported commodities, which may increase domestic revenues. A weak US dollar increases the price of imported commodities, which allows locally-produced commodities a better chance to compete in the domestic market.
Or as investopedia puts it:
An international traveler might harbor for a strong domestic currency because that would make travel to Europe inexpensive. But the downside is a strong currency can exert significant drag on the economy over the long term, as entire industries are rendered noncompetitive and thousands of jobs are lost. While some might prefer a strong currency, a weak currency can result in more economic benefits.