That's the goal tracing back to Eisenhower who wanted them to act like this so that America could sit back and relax somewhat. Creating NATO is not American's idea from very beginning anyway.
But in reality I don't believe any these countries can reach the goal of 5% of GDP except Poland (and tiny Baltic states who won't matter even increasing to 50%). Their slow economic growth rates, their commitment to wellfare such as healthcare, education, or social security...and climate protection, just don't allow them to have 5% military spending budgets. Mark my words, there will be social revolutions in most of these countries if they force to do it. Spain already has been given exception. They can reach 2.1%, instead 5%.