When there aren't enough miners, more will move over to start processing transactions. (finder.com)
If enough miners (the 51 % majority) agree to activate this new software instead of the old one, this can happen. (bitfalls.com)
Users may want one thing (say, faster transactions) and developers could build it (write the code and specification: a Bitcoin improvement proposal to allow for faster transactions), but if not enough miners support the proposal, it won't get implemented. (luno.com)