Why even offer bonus coins?

So I downloaded this app about 4 days ago and I noticed something reeeally stupid. For starters, it doesn't track all the walks I go on so I don't get rewarded for all of my walks. I walked about 36 miles in those days and only got tracked/rewarded for about half of the steps. Next, I noticed that the "bonus coins" or whatever from games give like 100x more coins than than what I earn from walking a little over 4.5 miles to/from work(over 9 mile walk round trip only nets me anywhere from 80-85 coins). And lastly, I just hit 3000 coins from both walking and from bonus coins and went to redeem them for an Amazon gift card only for it to tell me I need "500 coins from WALKING". If that's the case, why even offer free coins if I can't use em? It's stupid.