Synthesizing complex information from a range of technical sources enough to build bioweapons is cognitively impenetrable for the vast majority of people. The ability of AI to synthesize this information into a step-by-step recipe to follow is a step change in accessibility.

There's an opportunity cost to terrorism just like with any time sink. The effort to build up knowledge enough to produce some weaponized pathogen will be compared to just doing traditional terrorism. For some low capability terror cell, its easy to see how the cost/benefit analysis has been in favor of traditional terrorism up to now. The kinds of terror acts that take years of sustained effort to execute are rare. But as the barriers to entry to bioterrorism fall away and become widely accessible we may see the cost/benefit shift.