Hard removal could shut them down, because enforcers had to be on the board first before you could benefit from them. Now you can drop them down and immediately start to gun down your opponent. Even when ignoring balance, it's an awful change gameplay wise.
Initially, I thought the same. But when you consider that the nominal value for Bronzes is 12 - 14, it means the enemy needs to have at least 3 - 4 spies for enforcers to just be worth as much as any other bronze. which is not easy to happen, considering there are only 3 emissaries max. you need infiltrators and/or Ceallach too and even then, you will need 3 turns or more to bring them on the board probably. Meaning you have to go in a relatively long round to make them worth it without expending too much of the engine. Otherwise, the opponent plays some large tempo and they can crush you by the time you get the spies going.
In short, that change would have been absolutely insane before Midwinter. Now it's what's keeping the spies alive in the meta. Notice how none of their units, aside from the infiltrator, received any Strength boost, while everything is worth 11 points or more now.
**EDIT** Oh and don't forget that spies are only really worth it after the first engine unit. All the first one does is to make up for the points you give to your opponent via Emissaries