With the greatest of respect, I can think of literally 20 locations off the top of my head where carnage on a mass scale would be easier to inflict. As I don't wish to encourage or facilitate criminal behavior, I will decline to list them, but I'm sure you could come up with a similar list in minutes.
Do you propose we secure them all?
Morever, this (vehicular assault) is hardly the only way to cause destruction or loss of life at scale. Again, particularly in the current circumstances, I would feel uncomfortable rhyming off a list, lest there be one reader who mistakes it for a how-to manual; yet let me be clear that barricades against vans and trucks would only change a violent/criminal/terrorists m.o. not the result.
I don't want metal detectors everywhere, or fences, I don't want glazing to be routinely bullet-proofed, nor a heavy police presence everywhere.
I don't imagine you do either, but I think its a very fine line between imagining there's a useful investment to be made in 'defensive infrastructure' and a loopy amount of $$ going towards
a veritable police state.