In the beginning you get some results from some effort. However, as it becomes your new normal, those results slow, so you have to increase the challenge. Once you do that - either by increasing weights/intensity, duration and/or volume of work performed - you start to see progress again. Soon you adapt to this new normal, and the process repeats itself.
So weights get heavier, workouts get longer, and recovery gets more important - but your perception of how hard you’re working only moderately increases. That is to say, for example, 10lb bicep curls for 20 reps used to be an 8/10 on the exertion scale for you. Now, 6 weeks later, you do 15lb bicep curls for 20, but it’s still 8/10 on the exertion scale. It certainly feels heavier - you notice the weight - but it doesn’t feel 30% more challenging (the difference between 15 and 10lbs).
In short, it doesn’t get easier so much as you get stronger, fitter, and better able to manage the stress and load.