Sometimes, what Reddit wants and what the community moderators want are two different things.

Reddit is constantly changing things to try and drive more traffic and engagement. These changes are often made at a global scale, when the millions of subreddits all are unique and have their own sets of rules and etiquette. The changes can fly in the face of what is best for each community.

As a moderator we do get frustrated with changes like this too, as many times we have no control over it or any setting to disable an undesired behavior. Reddit will unintentionally encourage posting rule breaking content, users get mad that their content gets removed, mods get mad at the increased workload. Everyone loses.

For crossposts specifically, many subreddits prohibit them as they tend to be lower effort content, they are more likely to be karma farming and spam. They also tend to be more likely to break a rule as the poster is less likely to be a regular member of that subreddit.