DIY sensor vs off the shelf

Hey guys

First off, I'm sorry if this is a widely asked question, I'm really struggling with the reddit app...

Help me with some math here or component sourcing.

I'm seeing a lot of suggestions all over the place to not buy ready made tenp/humidity sensors and to simply build my own using an esp32 + sensor boards as it is cheaper.

I'm struggling to see the cost benefit when I can get a battery powered zigbee sensor for 4.2€/4.8$ on Aliexpress.

That price is the same as buying just the ESP32 and DHT22 in bulk (10pcs).

Is the main benefit not actually cost but a completely local environment with full control?