Most likely you wont get a universal artefact because inno want you to try hard on the specific event and when you only get 7, you will spend money to get the last 2 or so they hope.
If you had a universal artefact then people could then save the artefacts when they don't want to place one of the evolving buildings and then upgrade the next one without effort. Also with this never ending type event some people managed to get 30-50 artefacts they could then not participate in next few event and still upgrade.