that is because TestNet difficulty is designed a little differently than bitcoin's MainNet difficulty so that it can drop to 1 if it took more than 20 minutes to find a block. that way we can ensure TestNet goes on without getting stuck due to high difficulty and lack of hash rate.
but at the same time dropping difficulty to 1 means you can find blocks with your CPU (with a little hashrate) and if someone has a higher hashrate (like using their ASIC) they can mine a ton of blocks in a short time. that is why there are a lot more TestNet blocks now.
BTW, Is It Possible To Pre-Build A Transaction Before The UTXO Is Confirmed?
you mean spend an unconfirmed transaction? yes that is possible.
And, Where To Ask Question About Lightning Network(Are There Any Thread Dedicated To It?)?
open up a topic if you can't find the answer to any questions. asking in a dedicated topic can bury questions.