Why are they hiring people that need a visa and need to relocate across the world?

The ask for compensation for getting dropped before the start date should usually be an easy one for a company to accept since that shouldn't be normal operating procedures. Otherwise, they're aware that they're explicitly screwing over people and aren't serious about hiring. Now we're back at my earlier claim, and you dodged a bullet.

You don't need to be special, but you definitely shouldn't think of yourself as a cog in the machine. If you do think of yourself as a cog, or this is an offer you can't refuse, then you've already given up your bargaining power, and you are willing to accept this.