The reason for Tesla stock underperformance has now been explained by SEC filing that shows Elon Musk has been selling Tesla shares. The proceed can be used to help pay off Twitter’s $13 Billion loan which costs $1 Billion in interest payment. If this is his intention, then he may have to sell more shares to completely pay off the loan. This possibility of additional sales will be a drag on Tesla stock performance. At the beginning of the sale, Elon Musk had about 443,796,628 shares. At the end of the last transaction he still has a lot of shares at 423,622,432. This sale represent a small portion of his total ownership.
https://ir.tesla.com/_flysystem/s3/sec/000089924322038522/000089924322038522-gen.pdf