So i just checked this stats on Sia from the link you provided. What I could see:
1. from 2016 until now the token count is following the supply chart, which is 30+ billion. That's correct
2. If the token adds up with the chart, means there has been no any token burns. Or should this happen sometime in future? when? How much?
3. What is the inflation chart based on, any explanation behind it?.. don't get me wrong but i can make a chart like that also. What is it based on?
If no burn and max supply, the value will keep going down, because of constantly bigger supply.
Proof of Burn is not yet active, it is planned for next year. It will be a feature to prove that hosts are legit,thus avoiding Sybil attacks. No one can predict how many coins will be burned at a certain time: it will depend on how much each host decides to burn per TB and how many files are stored on the network. Thus, the chart is not considering PoB mechanics and it is showing the coin supply based exclusively on the block rewards (that is predictable)
Inflation chart just means what percentage of new coins will be in circulation 365 days after any time point. It is the same as the inflation indexes we see in FIAT coins. For example, checking today the inflation for the next 365 days is 25%. In other words: it will be an extra 25% of coins in circulation. In 2020 inflation will be under 4% meaning that in 2021 there will be a 4% more of coins circulating than in 2020. Again, inflation can't consider PoB as it is not predicatble, and it is purely based on the block reward.
Why so much supply? Sia developers strongly believe in Proof of Work as the mechanism to secure the network. You need a block reward in order to keep miners incentivized forever. However, as the block reward will be the same every year once it goings down to 30000, the inflation will be smaller and smaller (same new minted coins for a total supply that increases every year).