In many ways the Tanzimat reforms DID succeed in modernizing the empire, especially if we don't take the traditional end date of the reforms (the promulgation of the 1st constitution in 1876) and include Abdülhamid's and the Young Turk's continuing reforms, many of which were in the same vein as the original Tanzimat. If you want to look at just about any aspect that we would consider "modernizing," the Ottoman Empire made continual progress throughout the latter part of the nineteenth and early twentieth centuries. They enacted many liberal reforms (rolled back under Abdülhamid but reinstated after his overthrow), dramatically reorganized governance so that Istanbul was calling the shots, instituted widespread education for boys AND girls, instituted a modern conscription system that equipped their men with modern weapons (while the Ottomans lost wars like the 1877-78 Russo-Turkish War and the 1912-13 Balkan Wars, they also won some against Greece in the same period. And it's not like the Russians or Balkan powers totally steamrolled the Ottomans, there were several important successes for the Ottomans in each war, and the general consensus is they lost those wars due to poor planning and leadership rather than inferior arms), and the economy dramatically expanded. A lot of that wealth was funneled out of the country because of poor financial planning, especially immediately following the Crimean War, but that doesn't mean there wasn't a dramatic uptick in various economic activities, particularly in agriculture. Culturally, the Ottomans were training modern doctors, witnessing an explosion of printed materials, and engaging with the scientific discussions of the day.

I think the main difference is that while the Japanese were literally doing this on the far side of the world, the Ottomans were doing it in the backyard of the major European powers. When the Japanese defeated the Russians in 1904-1905, the Japanese defeated the Russian fleet. The Russians sent their Baltic fleet, which took SIX MONTHS to sail to Japan, where it was promptly defeated. Compare this to the Russo-Turkish War, where the main body of the Russian army was able to invade both sides of the Ottoman Empire at the same time. (Incidentally, the Ottomans were very much inspired that the Japanese had such success with their reforms, and the Young Turks used it as a motivational tool to demonstrate that they could, too.) The Austrians were able to annex Bosnia, because it was right on their border. The British could get to Egypt in 5 days under steam. The list goes on. In any conflict with the Europeans, the Ottomans were immediately under massive threat. Invading Japan was a massive logistical problem.

That is just the logistical difference. The Ottomans declared bankruptcy in 1875, after taking on a ton of bad loans after the Crimean War. The European creditors set up a Public Debt Administration that took first crack at Ottoman tax revenues to make sure the creditors got paid. This was on top of a number of unfavorable trade agreements known as the Capitulations. In early modern times, the Ottomans gave them as favors from a position of strength. By the 1800s, they were traded for European support, such as granting the British a massive break in tax on British goods in 1838 in exchange for British help against the rebellious Mehmet Ali Pasha of Egypt. Anyways, the Europeans had their fingers firmly in the Ottoman financial pie, which they could enforce because of their close proximity. This does not even take into account the practice of European nations giving their citizenship to local Ottoman Christians, which meant many of the most economically productive of the empire's citizens could not be taxed by Istanbul.

tl;dr: The Tanzimat reforms DID modernize the Ottoman Empire, but close proximity top Europe meant they could not escape ruinous European influence. Japan was far and relatively free to do what they needed to do. I would love to get a Japan expert in here to get that perspective!