From Alan Kent himself (eBay Search VP, M2 product technical lead):
SASS is more powerful than LESS, and appears to be gaining more market
share over LESS. So why did Magento 2 choose LESS? Sorry, a boring
At the time we had to commit to a technology, there were several
stable LESS pre-processors available in PHP, but no (stable) PHP
implementations for SASS.
The M2 team had put a lot of deliberation and thought into the long-term support of the product beyond the launch date and the amount of risk they were willing to assume. They also needed a LESS/SASS PHP compiler that was a specific license to be able to incorporate into M2. This posed an issue as the most popular PHP SASS compiler is a (somewhat) dormant project maintained by only one developer. Again, this was a deliberate process in the selection.
The CE 1.9/1.14 SASS implementation took a different path to implementation as it was a collaborative effort from 3rd party partners (Classy Llama and Brendan Falkowski) to license a pre-existing framework that Brendan had created and used on multiple builds, including the famous SkinnyTies.com implementation. This was already built in SASS and was to be repurposed by the 3M site build that is touted in the release announcement. 3M was Classy's client and
they contracted Brendan to help them deliver it while also being commissioned from Magento 1 team to make it part of the framework. The effort to deliver on-time was driven by the fact that the framework was already in-use and somewhat developed prior to the BF/CL endeavor. Long term support here is probably not such a desperate consideration because of:
- The proximity of the M2 launch (ETA some time EOY 2015)
- There is no runtime CSS compilation (M2 requires it)
- SASS is entirely optional. It is possible to use the new responsive framework without ever recompiling SASS.
<speculation>The decisions were seemingly made insular from each other.</speculation>