Just by virtue of providing the possibility of keys to the "Proverbial kingdom" and centralizing location of those keys gives far greater incentive for hackers or state actors to find new ways to gain access to these tools for decryption.
Depends on the systems connected to the private key of course, but billions per incident are certainly possible in some cases.
Even if this is just private chat on messenger platforms rather than 2FA or HTTPS, imagine how blackmailers would respond to getting all the nudes, the drunk confessions, the adultery, from 30 minutes access to all of the 10th most popular chat app in your country.