It is a mystery as to why, but we are generations deep into "all the kids today play soccer, they are going to grow up and watch it". It just hasn't happened. Lots of kids played soccer, but are now grown ups and have sports viewing tastes that are indistinguishable from previous generations.
Another mystery is that soccer playing kids tend to be, in the USA/Canada unlike the parts of the world where soccer is popular, from wealthier backgrounds, but this, too, does not translate into the demographics of who watches it as an adult.
Another mystery is that soccer playing kids tend to be, in the USA/Canada unlike the parts of the world where soccer is popular, from wealthier backgrounds, but this, too, does not translate into the demographics of who watches it as an adult.