why? the same reason that the current unions are ending up in disaster they got too greedy for their own good. no one wanted to pay their prices so they sought out independant merchants etc to do it for far cheaper.
of course the guildes back then used the same tactics that unions do now for non-union employee's and employee's not wanting to join the union.
they send their thugs to intimidate and harass people (all of which is illegal of course) which is why the unions want card check to begin with.
so they can send their union thugs to your house to try and threaten and intimidate you and your family into joining the party.
not all unions are bad the local unions that are not party to the national organizaions do very well for themselves and the employee's and the company.
very rarely are strikes inccured as both offer reasonable demands that can be agreed to.
in this case however the union cost people jobs that they otherwise would have had.
PS if you are so up in arms about card check why don't you go rail on media matters which rejected the same process.