[s_tec]

The tangle fails to to the one thing a blockchain needs to do - prevent double-spends. Rather than give up their failed experiment once they realized it didn't work, the IOTA project instead set up centralized "coordinator" nodes to prevent double-spends, since their tangle data structure was useless.

Now, there are ways to build graph-like data structures that do prevent double-spends correctly. I believe both Hedera and Nano (formerly called RaiBlocks) have working solutions, for example.

The key is that not just anybody can create a block (or a graph node), as IOTA does. If anybody can create a node at any time, what prevents them from sending out contradicting messages? Instead, working solutions always involve putting some sort of asset at risk (such as currency or energy), so that if the block producer decides to make a contradicting statement, they pay a steep price. This ensures that there is a financial incentive to always work towards consensus.