A lot of people are attributing the decrease in fees seen as of late to the increase in segwit adoption. Whilst this is partially true, there has also been a number of other factors at play that have lead to a big drop in fees.
[1] Many exchanges have started bundling transactions together to reduce transaction sizes, this is arguably the real reason for the low fees we see, as exchanges we responsible for most of the network spam we had to deal with last December
[2] There has been a spike in mining power dedicated to bitcoin, as Bitcoin rallied faster than other cryptos people dedicated their ASICs to BTC pools, rather than mining upcoming altcoins that had the potential to appreciate faster than BTC
[3] There are simply fewer transactions now. Here you can see that there has been a significant drop in n transactions/day, decreasing from a peak of over 400,000tx/day to under 200,000 as of April 2018.
https://blockchain.info/charts/n-transactions - This means less competition for blockspace, and hence less tx fee gouging by the miners.
[4] The advent of some lightning wallets has moved some transactions off chain, this probably accounts for a very small part of the reduction we have seen.
That being said, there is a slight increase being seen recently, as I have seen up to 30sat/byte being necessary for the next block at peak times.