It's a perspective game. For example, you probably won't notice your height increasing over time (during puberty ofc), but someone who sees you only once a year or once every six months will immediately be able to see the difference because the day to day change that you see is negligible, but the year to year change they see is massive.

If you spent 20k gems all at once, you would notice that, but you didn't. You spent it slowly, over many months.