Patent offices don’t really check for prior art. There’s a short period between patent applications and patents being granted where the public can submit prior art. If nobody notices that such an invalid patent is being applied for and thus nobody submits prior art, the patent is granted. Patent offices are of the opinion that it’s the responsibility of courts to sort out invalid patents like that.
Patent litigation is super expensive and time consuming. So if a huge corporation like Stratasys holds a patent, most smaller companies (and yes, in this context Creality, Prusa and Bambulab count as small) usually don’t want to spend all the time, effort and risk of a patent fight. Also, even if you win, you don’t get your legal costs back. So even if e.g. Prusa fights Stratasys over that patent and wins, Prusa will still lose all the money they spent on legal costs for the lawsuit. All over a feature that, while cool, doesn’t bring them any money at all if they implement it.
That’s a core problem with the patent system: