We only have delta because people did not either take precautions (masks, distancing), get vaccinated, or both.
The evolutionary mechanism of viruses predicted this outcome. Selective pressure (vaccines) enhanced the evolution.
https://odysee.com/@DarkHorsePodcastClips:b/Natural-Vs-Vacci...
Your vaccine can prevent some serious cases and reduce your infection rate but it makes it more likely that you are an unaware carrier and super spreader.