Why doesn't Allah answer my prayers, and why do I not succeed in worldly matters despite my repentance, frequent supplication, taking the necessary means, relying on Allah, and seeking His guidance?

Your conception that repentance directly leads to bliss and the removal of affliction is incorrect. Life is a trial and a test, and true bliss is the bliss of the heart and certainty in Allah. "Whoever does good, whether male or female, and is a believer, We will surely grant them a good life." Some err in supplication, thinking that it is answered merely by making the supplication, or that the answer is of only one type (the fulfillment of the request). Supplication has conditions and impediments, and the answer might be the averting of evil or the storing up of reward. A Muslim's deficiency in obedience might prevent the answering of supplication, and this should motivate them to increase their closeness to Allah.