90% of bitcoins being hoarded as investment or used for day-trading in exchanges, rather than used as currency for payments.

Investment funds that use bitcoin as the backing asset.

Extreme price volatility, which makes the coin unsuitable for use as a currency.

Main uses of the coin as currency being online gambling, purchase of drugs, ransomware, ponzis and other scams, and other illegal payments.

Concentration of mining in ~20 companies, of which ~10 have >80% of the hashpower.

"Full but non-mining relay nodes" sitting between simple clients and miners and presuming to act as "volunteer vigilantes" over both sides.

Trafic growing more than 50% per year (up to 100% per year) for 2-3 years in a row.

The network being congested (intentionally!) with transactions delayed by days, unpredictably.

Hundreds of altcoins, most mere clones or trivial variations on bitcoin, that do not seem to go away.

"Bitcoin banks" -- services that hold bitcoins (real or virtual) for customers, like Coinbase, Xapo, etc..

Numerous large thefts by exchanges and other services.

One company intending to decide the future of the network and dictate miners' revenue.

The community split in a bitter war over a totally banal maintenance patch.