Because tariffs are supposed to be strategic based on economic need.
Blanket tariffs with no eye on the impact the economy is a bad policy. If for example, importing lumber that was cheap from Canada ruined the lumber market in the US, then a tariff to help that balance where US lumber companies could still operate here, then you add a tariff. That's not what happens though. Lumber in colder climates grows stronger so it is a benefit for the US to be able to purchase that lumber as cheaply as possible as America would not be able to produce the same quantity / quality.
It has to be targeted and strategic to make any sense. Just like Canada does not have a blanket tariff on US goods, they only impose a tariff on goods that they need to be able to produce in their country so they don't lose jobs and industries.
It does not help us whatsoever to purchase lumber from Canada at a more expensive price.
Also, announcing tariffs and backing off a couple days later and then doing the same exact thing a month later is just absurd governance if we're being honest here.