AOPA has asked the FAA for consideration for these types of situations. As of right now we haven't received any answer. Keep an eye out on the website front page, as that is where this information will be posted when we hear back.
Why can they not extend our flight reviews for 90 days? This should not be that difficult
It's not so easy to change a regulation. Some regulations can be waived, such as many of the Flight Rules in Part 91. But those waiverable rules are specifically listed in Part 91 Subpart J, along with the procedures to waive them, and all other Part 91 rules cannot be waived (and that includes 91.409 for annual inspections, which isn't on the waiverable list). For Part 61, there are no waiverable rules, so the only options would be to change the rules or provide an exemption to those rules. The FAA isn't going to change the regulations just to meet this one situation (and even if they wanted to, the process takes months to years), so that leaves only an exemption. The exemption process is described in Part 11, section 11.61, et seq. As you can see from those regulations, this isn't something which can be done by waving a magic wand. Typically, you need 120 days lead time to get an exemption. No doubt the FAA can speed that process if the need is urgent, but it won't happen overnight.
Note that with the medical certificate issue, the FAA didn't change the rule, but only announced they would not enforce the rule for a period of time. Perhaps they could do the same thing with recent experience and flight reviews, but there are other issues to be considered. With medical certification, the FAA has always put the responsibility on the individual pilot for deciding on a daily basis whether you are fit to fly. But when it comes to issues of flight proficiency and recent experience, I suspect the FAA views proficiency as a more perishable commodity. We'll see what they do.