This makes the stock price in line with other dow jones stocks, something that Apple did right before it was included in the Dow average. The Dow unlike other indices does not weight by market cap or anything like that it literally uses the stock prices.
Increased liquidity. Also option trading is usually in 100 share units, meaning retail investors can now afford more options (e.g. $15,000 vs $300,000 a unit).
Anecdote warning:
This is one reason I have not been able to buy/sell google options. (I did around Brexit when google was 650 or so, but not since). Even a single contract is a massive risk for a layman portfolio like mine. 1/20 will imply I will definitely attempt to trade this.
It's not only psychological -- for example, a lot of brokerages don't offer fractional shares, so a split allows some retail investors to invest who couldn't afford to before. (Although that almost certainly has a smaller effect than the options contracts etc mentioned in sibling threads.)