There are many reasons for the network hash rate to have increased, but IMO, a Bitmain ASIC conspiracy ain't one. Daily media hype towards the end of last year, $20K BTC and $1300 ETH, which on a yearly basis outperformed BTC by almost 10000% a the end of last year and beginning of this year brought in lot's of new miners at a peak, as it always does. Another factor that limited the network hash rate was the ETH ICE AGE MAY-OCT artificially increased block times and difficulty. Once the Byzantium fork happened in the middle of OCT it ended the ICE AGE and profitability increased right around the time Crypto started the end of the year bull run, which brought miners back to ETH. The most recent hash rate increase is from Vega miners switching to ETH after a collapse in Cryptonight profitability.
I gave you merit on this, its basically a turn of events, I do also mined XMR at ICE AGE however it started at the end of the year when ETH is way more profitable than mining Cryptonight, when Vegas were out and GPU shortage happened medium type GPU's like Rx550, were forcibly sold out and guess what, they also added to mine ETH.