Why wait until you see we get low to offer free coins? Outside of videos there aren't many options. When new you may not win much to help boost coins. Almost any other game gives you at least something for a daily login (coins, boost, etc).
The coins should regenerate up to a set amount each day. If you are ever looking to boost them you can go into the store screen and use the Watch ad button for free coins.
Stephie Vee commented
They added rewards for duels--coins and power-ups.