What could the reason be why there are not so many prominent trading bots? They seem to make traders' lives easier.
Bots seem to function best under conditions where identical commodities are priced differently across different platforms. Example under HFT if a bot sees microsoft stock priced at $68.94 on one exchange and $68.59 on another it can almost instantaneously buy the $68.59 on one exchange and sell @ $68.94 on another. In the stock market under HFT (high frequency trading) they have an entirely different high speed electronic trading pool (dark pool) set up to make it easier for this to happen.
BTC and altcoin trading aren't structured in a way that would allow that type of high speed HFT trading. There is no high speed method to trade/transfer btc or alts between different exchanges. The high percentage fee for exchange withdrawal also is the opposite of HFT and dark pools which have very low cross platform trading percentages by contrast.
Bots in crypto can be less profitable than a buy and hold strategy.
In btc's move from $1200 to $1600 a trading bot could easily have sold at the wrong time which could give someone less profit than had they simply held btc.
A lot of bot trading strategies depend on daily price fluctuations to generate profits. Looking at some altcoin price movements, there are days where prices won't fluctuate more than 1% to 3%. Using a bot to try to take advantage of those percentage-wise small price movements can be a bad strategy for many different reasons.
All of these reasons and more are probably why bots won't see heavy usage anytime soon.