The other post is wrong for so many different reasons but highlights the lack of understanding of agriculture that is far too common on Reddit.

It started when seed companies found that hybrids between different strains were the most successful (where success might have been environmental tolerance, disease resistance, yield, etc) but that success is only true with the first generation of the crossing, the so called F1 hybrid. You could save this seed and re-use it but it would be a bad idea, typically the next generation (denoted as F2) would have none of the desired attributes of it's parents and many times would be worse than either of the original hybrids parents strains. The only way to keep that success was to buy new F1 seeds each year, and only seed companies are going to bother with the intensive requirements to make said seeds.

Next you have the issue of what is thought of as GMO strains, where (at least for the first strains released) the first seeds were not hybrids and would remain true if replanted. However as there is no way the seed companies could recoup their investment, they changed models to something more akin to a subscription for the acres you wished to plant for each year. You could theoretically keep this seed and use it, but you still would need to pay your yearly subscription for the right to plant it.

These GMO crops can also be hybrids, but the two are not one and the same.