It's the combination of a simple tool type (many free and proven alternatives), a relatively professional usage pattern (many potential users already set up with something good enough) and, I'm afraid, lack of compelling novel features that are worth testing and/or paying for and/or taking the trouble to use something other than a general purpose image editor for. Some specific features are perplexing: where is lossless PNG recompression, with size benchmarks? How do you convert PSD and raw formats to simple images?