The need for a big battery comes from several potential issues:

Do you ride in cold weather.  A larger capacity battery is needed if you are going to start the bike when it is cold (battery performance is down, oil is thick, etc).

Do you make lots of stops/starts when you ride?  The charging system is not very robust and it takes a while to recharge the battery after a start.  (A few members have run their battery down when they make lots of short trips).

Does your bike start quickly?  A bike that has to crank for a while can run the battery down and a longer ride will be needed to recharge it.

And finally and maybe most important - you need enough cold cranking amps to keep the battery voltage high enough to run the ignition system.  If too much of the battery power is going to the starter and the voltage drops - you won't get any spark and the bike won't start.

Although Lithium batteries are expensive and have their own set of issues - they are small and lightweight and able to provide full voltage to start the bike (when they are not cold).  If you are after small and light....they are able to provide that.  Lithium  batteries are ruined if you let them run down completely - a lot of the better brands have a safety built in that won't let you run them down low enough to be damaged...they disconnect when the voltage gets low.