You are comparing EVE to a game that is fundamentally different - Escape from Tarkov is a FPS Battle Royal style game. What works for one game does not necessarily work for another. Having a “PvE” server of EVE would simply not work, mainly due to EVE’s 3 pillar system (Resource Gathering > Production > Destruction) which requires asset destruction more or less equals the production otherwise the Economy would fall apart.
It’s not about the cost of running the test server. Access was cut off mainly due to Test Server (SISI) being mirrored from live server (TQ) and for that reason access to it was being exploited for gathering intelligence on structure locations. Thus having access to SIS, by alliances/coalitions, it had major impacts on activities taking place on TQ.
As has been explained in the other thread on the subject of SISI, it exists only for the benefit of CCP testing new features before they go live - not to the whims of players.