In very simple terms, big tech corporations (though many offer seemingly “free” products) make huge amounts of money out of products which often are available (but way less advertised) as an open-source counterpart. This huge amount of capital taken out of the common people is then used to invest in assets, inflating them and outpricing us. Conversely, the open source movement is about working for a common good, empowering both developers and users by keeping the product of labor from being capitalized and funneled into billionaires.
*Sorry for my English, as it's not my first language.