NPOSL is an Open Source license; you've made a common reading error with the license text. It's the licensor, not the licensee, that needs to be a non-profit. In other words, a non-profit could publish code under the NPOSL, but everyone else can use the code.
The NPOSL is a variant of the OSL; the OSL's author explains the license on their website:
There is also a new Non-Profit OSL 3.0, identical to OSL 3.0 except that: Under Non-Profit OSL 3.0, Licensor disclaims certain warranties and limits liability from certain types of damages. Those differences are summarized in § 17 of the Non-Profit OSL 3.0, a section that does not appear in OSL 3.0 or AFL 3.0. Because of § 17(a), only non-profit distributors may use the Non-Profit OSL 3.0 license.
Reduced Risk For Non-Profit Organizations
Some licensors are non-profit organizations that derive no revenue whatsoever from the distribution of the Original Work or Derivative Works, or even from support or services associated with those works. As a simple economic matter, these organizations have no revenue stream and they cannot afford to offer any warranties, even a simple Warranty of Provenance. For those licensors, there is now a Non-Profit OSL 3.0 that doesn't include that warranty and that disclaims liability even for direct damages. The differences between OSL 3.0 and Non-Profit OSL 3.0 are detailed in § 17 of the Non-Profit OSL 3.0 license. Section 17 includes Licensor's representation that it is actually a non-profit organization. Note also that once an Original Work is distributed by a Licensor who cannot make that non-profit representation, the license reverts to OSL 3.0.
tl;dr if you redistribute NPOSL code and you are not a non-profit, the license reverts to OSL (clause 17 (d)). The license is designed to protect non-profits, who by law cannot provide some warranties that the normal OSL requires.