Let me quote Google:
“If TensorFlow is so great, why open source it rather than keep it proprietary? The answer is simpler than you might think: We believe that machine learning is a key ingredient to the innovative products and technologies of the future. Research in this area is global and growing fast, but lacks standard tools. By sharing what we believe to be one of the best machine learning toolboxes in the world, we hope to create an open standard for exchanging research ideas and putting machine learning in products”
So do we think that it requires a common platform on which innovation in the field of FPGA programming can happen. And for economic and strategic reasons, this common platform must not be owned by one private company, but need to be a common good, open and hackable and affordable for everyone.