1. In real life, at work, there is very little use of mathematical proofs. Even in scientific research, the so called proofs are defined as preponderance evidence and elimination of false arguments.
2. Finding answers is a more important skill than rigorous proofs. Estimation, inventing ways to calculate are more important skills than proving in practice.
3. For improving thinking skills, proving mathematical thereoms requires demonstrating an answer given by others. It encourages rationalization rather than finding out truth. It encourages being passively pushed by others than active pursuit.
4. For education in mathematics, finding an answer and later justify and make sure the answer is right itself involves proof. I'd say finding and justifying answers requires more complete skills than proving.
5. Again, for education in mathematics itself, understanding the importance of mathematical problems, keeping the curiosity of exploring mathematics as a subject is more important than proving. Even Euler sometimes was not that rigorous in proofs.
6. I am not saying rigorous proof is not important. But it mainly belongs to a chosen few, who really requires such skills.