The information may be as reliable, but:

1. the service may not be - every small provider has downtime, perhaps proportionally to their size.

2. the tools to update Twitter are well understood, and you can get software that does scheduling of posts across multiple platforms, previews of what posts will look like, etc etc, and said preview works well on the many platforms that people are already using. People doing the updating may prefer to use those tools over what the internal tool gives them.