Hmm if it has to do with taxes here, I'd expect a lot of purchases around now (late March/early April) when all the tax refunds come in.
Alternatively maybe people have been dumping fiat into cryptos right before the end of year to avoid paying some taxes? I don't understand tax law well enough to say.
The pattern is there, however, and it seems to correlate with consumer trends like Christmas and Chinese New year. Maybe it's just a sign that cryptos are viewed more like consumer goods than as currency right now?