And this isn't even relevant to what is happening with Booking.com. No one is being explicitly fired, they are being moved to a new company with different job requirements. Which as far as I understand, is constrictive dismissal, so the right thing in this case is for Booking.com to give all their employees the option of being laid off instead.
Notably, the Reddit poster is from France, so this sin't a "US vs Europe" thing as some other comentors are trying to make it out.
Also, looking at https://www.iamexpat.de/expat-info/social-security/unemploym..., seems unemployment in Germany is similiar, but in some situations less than in the US- though it can also, in some situations, last longer.
Meaning, it does happen, but it requires the workers and union to accept it actually takes place, the company cannot just decide on their own that they will do it and that is it.
They've just pulled the rug from underneath you without it being your fault in any way.
Therefore you cannot just fire 200 people to hire another 200 cheaper, because that's a way to increase only company's profit but not society benefit. And if you fire them, you need to compensate them properly. Of course companies try to go around these regulations, it's up to each Government how to enforce laws to prevent it.