According to the manufacturer, this is a type of boundary-layer microphone with deliberately reduced low-frequency response, designed for use in public address systems (i.e. not music recording).
Normally we are taught to keep microphones a good distance away from room boundaries to avoid comb filtering effects (some frequencies irregularly exaggerated while others are canceled out, as a function of wavelength). But BLMs reverse this logic and use the surface that they're mounted on as a deliberate part of their acoustical design. For good low frequency pickup, they require a large, flat, rigid mounting surface immediately behind them--no exceptions. Otherwise they'll have a 6 dB drop in their low frequency response, starting at some frequency that depends on the dimensions of whatever's actually behind them. If they're not mounted on such a surface, their mid- and low-frequency response becomes irregular due to reflections and cancellations--as I said, the logic of normal mike placement is inverted in this respect.
The thing is, most common stereo live music recording setups don't, and can't, work that way. On top of that, these A-T mikes appear to have a further low-frequency rolloff or cutoff built in, because (to repeat) they were designed for speech pickup. (For the frequency range that they have, they wouldn't need AS large a backing surface, simply because they have no significant output at lower frequencies. BLM designs overall are generally more practical for speech applications than for music, with very few exceptions.)
A more subtle consideration: When the manufacturers design directional microphones for close pickup of speech, they often use shorter measuring distances when specifying the frequency response (e.g. 30 cm instead of 1 m). That is arguably legitimate IF you assume that buyers will limit themselves to the applications that the manufacturer indicates. But if you or I try to record music at a more normal pickup distance with microphones that have been specified in this way (close-up measurement), we won't get the proximity effect that was baked in to the specs and graphs. So we end up with substantially less low frequency response than the numbers and/or graphs indicated--even though that was already quite restricted. For example A-T's lower limit of 70 Hz for this microphone (probably the -3 dB point) might be more like 120 or even 150 Hz at a normal recording distance, just as a rough estimate.
All in all, I would say, "whoa, boy" ("whoa, sir" or "whoa, ma'am" if "boy" has severely negative connotations for you).