You asked "As a postscript, any thoughts as to why in the case of addictions, ERP wouldn't reduce anxiety buildup?"

Actually, exposure and response prevention makes a lot of sense with addictions when the individual has been using substance abuse for short-term relief of anxiety or when cravings are a problem. If it is possible to get the individual to face situations that trigger anxiety and/or cravings and tolerate the anxiety/cravings until they pass rather than using their substance to relieve the anxiety/craving, this can be quite useful. Repeated exposure and response prevention should diminish the anxiety and/or cravings and decrease the likelihood of relapse.

However, this can be tricky. It is not easy for individuals with a substance abuse problem to tolerate intense anxiety or intense cravings without giving in and turning to their substance for relief. Obviously, we don't want to trigger a relapse by putting a recently abstinent client into a situation that they can't handle. Personally, I'd be fairly cautious.

My leaning would be to consider this type of intervention only if the client was fairly stable, had a fairly high level of motivation, and had adequate skills for coping with anxiety and cravings without recourse to substance abuse. I'd want to do initial exposure and response sessions in a controlled environment where substance abuse isn't an option (i.e. therapist's office, treatment program, etc.) and I'd want to make sure that we've set aside enough time so that there's time for the anxiety or craving to peak and come back down to near-baseline levels before the client leaves. (It might not be necessary to be so cautious but I don't have a lot of first-hand experience with this so I'm going to be cautious)