I AM NOT A LAWYER.
THIS IS NOT LEGAL ADVICE.
It is not certified by either FSF or OSI. The process of getting it evaluated by the OSI and certified involves a lot of money, unless it is such a popular license that the OSI is politically backed into a corner about it. The FSF's politics around such things get downright strange; I'm not even sure what it would take for the FSF to consider a non-GNU license.
AL2 contains restrictions such as a requirement to perform bookkeeping when making changes (notes for every modified file about who changed it) and restrictions against changing another file. The bookkeeping restriction is violated with stunning regularity; so far, nobody has been sued over it, as far as I know, but that's true of the majority of license violations anyway.
AL2 also, as I mentioned, has some serious license incompatibility problems. Some patent and indemnification material in AL2 is considered incompatible with GNU licenses prior to v3, for instance. In fact, any license that includes a restriction against any connected work being "more restrictive" in some way (which includes GNU licenses, among others) is likely to suffer some significant compatibility issues with any license that has weird quirks like the previously mentioned issues of AL2 (bookkeeping, invariant file), too. The patent termination part of AL2 is unlikely to cause incompatibility with most licenses (GNU licenses are weird, in that regard) unless they come with a restriction on "restrictions" and have a less restrictive patent clause than AL2 (no patent termination, for instance), but the edge cases in AL2 can cause issues with other licenses.
I'm not a lawyer (and this is not legal advice), but I think a case could be made in court that AL2 and GPLv3 are actually not compatible at all, because of those clauses, despite what ASF and FSF say.
Beyond that, there's just the simple fact of complexity. You've probably heard that software tends toward X bugs per Y lines of code, and that's true for the most straightforward, linear software designs. As the complexity of the design of the software increases, though, the possible unexpected interactions between parts of it increases as well. The result is that, in practical terms, the likelihood of bugs actually increases faster than the number of lines of code. The same effect occurs with legal licensing terms, to some degree; the more complex a software license, the more likely you are to run afoul of unexpected legal effects of the license. AL2 is a rather complex license, much simpler than GPLv3, but significantly more complicated than something like the COIL, especially given the inclusion of the terms I mentioned earlier, which are radical departures from the most widely-used, best-understood "state of the art" of license design.