Those projects and the blog post are describing the behavior of Limit Order Books. Of course when you have real-time you can monitor each and every change of those and see how things are executed (and even estimate how things are going to be executed)
Not bearing any relationship to timeframes (minutes, hours, ...), because you see every change (ticks) is the problem.
Let's imagine the scenario:
You pass 1-minute data to backtrader
A set of indicators gives you the signal to enter the market long (buy)
You fire the order in backtrader
And this is what happens:
backtrader gets the next 1-minute bar
And it tries to see, depending on the execution type, if the order can be matched against the range of prices from that bar
With, for example, Limit orders:
The matching price can be at many points in the bar
Now the question:
Are you going to provide a Limit Order Book for each an every possible price in the 1-minute bar? (Luckily it's not an infinite number, but depending on the range it can be a huge amount of entries in the Limit Order Book)
From a practical point of view the cost of the transaction and simulating the ask-bid spread effect can be achieved by including slippage (which is already supported by the broker)