When big banks, businesses and all the poor unbanked (cannot pay BTC on-chainfees - but BCH) ?
what are you talking about? the current bitcoin transaction fees are about $0.15.
edit: typos
Many of us doing on-chain bitcoin transactions in late 2017 until about January 2018, recall how the BTC transaction fees went skyrocketing up - actually, there were several times in 2017 in which BTC transaction fees went skyrocketing up. Coupled with fees going up tended to be longer BTC transaction times.
Large fees and longer transaction times was a narrative that the BIG BLOCKER nutjobs wanted to push, and also the alt coin pumpers had some incentives to propagate such narrative to pump their shit by suggesting that BTC is broken or inadequate and that other Bitcoin 2.0 systems (aka alt coins) would be the solution for such problem.
The most reasonable inferences from the evidence remains that spam attacks were occurring on the BTC network to attempt to provide evidence for the made-up bullshit narrative, and even though it remains a bit unclear regarding the culprit of the spam attacks, largely it is attributed to folks like bitmain, Roger Ver and coinbase, even though there were likely some others that were contributing to acts and practices that added to the clogging up effects of the spam attack of the bitcoin network.
By the end of January or so, it became more apparent that the cost of the ongoing spam attack and even the actual ongoing effects of such spam attack were becoming greater than the benefits of keeping such spam attack going. Yeah, there was a bit of a risky (but seemingly justified) move from bitcoin node to expedite the live activation of lightning network - which would then more quickly negate some of these projects attempt to maintain their claims about BTC's alleged high transaction fees and slow transaction times.
So, yeah, ever since the end of January the spam attacks largely stopped and any further attempt to reinitiate such spam attacks have not been effective which brought BTC fees and transaction times way down into relatively low ranges, which can cause some concerns regarding whether if such low fees were to persist, then are there enough mining incentives built in... but that sustainability (and incentives) of low fees scenario remains largely offset by relatively lucrative mining rewards that will continue to be decent for a few more halvenings.. so perhaps the fees could stay relatively low for 10 or 20 more years, but likely as BTC adoption increases, fees are likely to naturally go up, too... and yeah, it does seem to become more and more expensive to engage in bitcoin spam attacks, but likely those spam attack times are not behind us - even though they might have to be more strategically employed as compared to the 2017 to January 2018 period that they were employed for months at a time (December 2017 to January 2018 was about a two month long attack).