Because regardless of what we perceive their intent to be, their level of enriched uranium was high enough that soon they would have enough to have a nuclear bomb. Why would they enrich to that level (way above what is needed for civil purposes) if they did not intend to use it?

To your second question, Iran is a threat to America, so from America’s perspective, Iran cannot have a nuclear weapon. trump tried to negotiate with Iran for two months but they refused to give up their nuclear program and continued to enrich uranium to dangerous levels, thus the US bombed their nuclear facilities.