It's the same with most services that rely on diversity of demand.
Trains, buses, taxis, electricity, phone, internet and brokers are all fundamentally the same. They rely on the (normally correct) notion that not all potential demand will be there at any one time. For example, we won't all turn on every appliance all at once - the grid
will fall over there and then if we try. Same as it's assumed that not all customers of any given broker will try and sell / buy shares at once.
The only real solution, and I can hear the howls of protest already, is either very heavy handed regulation, outright government ownership or creation of a single monopoly broker legally obliged to serve all. Either way, get set for $100+ brokerage on every trade.
I've never seen
any non-government company intentionally invest sufficiently in order to cover the maximum peak in demand (for anything) whilst allowing for some routine equipment failures etc at the same time.
It's just not profitable to invest heavily in infrastructure that will at best be used once or twice a year and more likely once in a generation.
So Etrade doesn't work on a day of moderately high demand. Just as you can't find a taxi on New Year's Eve and the privatised power companies are bailed out with physical supply by their government owned rivals interstate every time there's high demand.
Reason for all of this? It's just not profitable to meet all possible demand be it for brokerage, taxis, power or anything else. Government will do it for broader economic and political reasons, private enterprise won't because it's not profitable
for them.
Give us a proper market crash and I'd be highly surprised if there's
any broker that meets all of thier customers' attempts to buy or sell. Indeed the ASX itself could well lock up under that scenario - odds are they haven't invested in enough infrastructure to cover an outright crash and the huge volume that would generate. The ASX is itself a profit making business after all.
Solution? Either be a high enough volume trader to get very good service from your broker or plan your trading / investment strategy to cope with the inevitable. For most, the latter is the only viable approach.
Nothing is totally reliable. You can have dial-up, wireless broadband and satellite internet. You can have mains power, an inverter with a room full of batteries and a generator as well. You can have 3 computers. You can have an armed guard standing outside your house to protect it all.
Then the whole lot is destroyed when the house burns down.
And the next day the market crashes.
You can't guarantee absolute reliability.