The style attribute isn’t allowed in Discourse because it could easily break things.
Also, Discourse has a certain philosophy on how information show be presented in posts, and limits tags and attributes on purpose.
The align attribute on <div> is explicitly allowed here: discourse/allow-lister.js at main · discourse/discourse · GitHub
If you were to migrate a forum and wanted to keep some special styling like colors, I’d go with Discourse BBCode and edit the importer if needed 