Little inventors might like to shop an idea first and then file a patent application if they find traction or funding. US law allows for a one year grace period after disclosure. Fail to file within one year, all US patent rights are lost. Outside of the US, any public disclosure before filing bars a patent.
Big Corp has the money to file patent applications early before disclosure.
Now with first-to-file in the US, there still is a one-year grace period in the US, but the first applicant to file is the winner not the first to invent.
Among other things, this is bad for small inventors because bad actors can file patent applications on the small inventors' inventions first. Trolls can and do scour websites to identify inventions that may be worthwhile sniping. In the old days the inventors just need to show that they invented their invention before the troll filed their patent application. Now, you have to prove that the troll literally stole the idea which the USPTO doesn't really look into.