Even if you trust Microsoft not to keep it, not to access it and index it on their cloud, and even if they were kept encrypted and local, it is still searchable

Even if you trust Microsoft not to keep it, not to access it and index it on their cloud, and even if they were kept encrypted and local, it is still searchable and index is available on runtime. So you have yet another process that has this unencrypted in memory. Great target for malware no matter what.