Mining with Prof of Work (PoW) behaves like a lottery. Almost every week you have a winner of the jackpot, but you can play for years without winning once.
The probability of winning the jackpot is extremely low. The reason that every week there is a winner is the huge number participants (total number of lottery tickets sold).
You as a solo miner have one ticket with every new block of this lottery (about every 15 seconds), but there are several thousand other miners that have one or more tickets too. The calculation power, of the miners hardware decides how many tickets they have in the game. Other miners have just more hardware in the game, so it is like buying many hundred or maybe thousand tickets.
This leads to the situation that you need months to win once. Other gamers have just a higher probability than you.