Re: Fees have been low after Segwit's growing adoption. Thanks Segwit.
Additionally technology such as LN and Schnorr Signature also makes transaction fees smaller and transaction size reduced 
LN does nothing to transaction size at all or transaction fees directly.Schnorr does.
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technically speaking the fees went down because of 3 main reasons which i will list in order of importance effect:
1. spam attack against bitcoin network stopped for whatever reason: maybe because SegWit was activated finally, maybe because BCash went away, or maybe because Dash and other altcoins that were spamming got dumped hard. but the spam attack stopped.
2. price became more stable, specially in the past 4 months. and without huge rises or huge falls there is always less transactions on the network.
3. with SegWit we got about 20% capacity increase (so far) which helped a lot and also some of the big services started batching their transactions which improved things a lot too.
1. spam attack against bitcoin network stopped for whatever reason: maybe because SegWit was activated finally, maybe because BCash went away, or maybe because Dash and other altcoins that were spamming got dumped hard. but the spam attack stopped.
2. price became more stable, specially in the past 4 months. and without huge rises or huge falls there is always less transactions on the network.
3. with SegWit we got about 20% capacity increase (so far) which helped a lot and also some of the big services started batching their transactions which improved things a lot too.
4. Exchange/services (such as Coinbase) uses batching transaction which reduce tx size
5. SegWit actually use block weight limit which enable higher block size (a bit higher than 2MB actually on most cases)
both of these are included in #3 that i mentioned. i didn't want to put batching in another number since it was not some separate thing.
as for SegWit block size, it can be a lot bigger but it is currently not. based on its adoption the size of blocks is usually around 1.2 MB which is that 20% increase i mentioned.