Mojang’s “stealing” started from at least the pistons in 2011, 3 years before the acquisition. Credit was given to the original mod author under “Additional programming”, and they did reuse the actual code from the mod

I don’t think it’s fair to call that stealing, for multiple reason:

• copyright of game mechanics should never be supported, if we serioussly consider this stealing then a lot of innovation will be completely hampered, and videogames will be subject to abuses worse than what exists in other creative industries. Copyright on game concepts would be akin to copyright on camera angles, special effects, etc…
• mods are only available on PC. Taking ideas from the community and incorporating them into the base game makes the content available for everyone, even vanilla PC players
• Mojang’s has been very decent with OG mod authors, often being assisted by said authors to incorporate their content into the game, see how they worked with the author of Mo’ Creatures, a mod for animals, to add the horse into the game