Russia collapsed because its economy was basically extractive - based on plunder of natural resources and ruthless exploitation of peasantry - with little or no investment and thus reproductive power (the Soviet system was basciallya remedy to this situation by implementing a state sponsored investment system). By contrast, a truly capitalist system can reproduce itself (which is not to sya that it does not exploit those who provide labour power for that reproduction) - and that makes all the difference vis a vis quasi-feudal systems such as tsarist Russia.
As Barrington Moore (and others, such as Dietrich Rueschemeyer, Robert Brenner, or Alexander Gerschenkron) splendidly argued - a revolution (i.e. breakdown of the governance system) is essentially a phenomenon of rural societies (such as Russia or China) ruled by backward elites that failed to keep up with modernization. Facing an increased military pressure from abroad (mainly from countries that did modernize), these elites responded in the way that they always had beed - by increasing exploitation rather than by modernization.
Russia is a prime example - there were numerous attempt to overhaoul the feudal system since the mid 19th centure, evidenced, inter alia, by several attempts on the tsar lives, and tsars ' moderate attempts to curb the power of landowners by abolishing serfdom in 1862(?). But that was not enough - as evidenced by a Russo-Japanese war of 1905 during which the Russian fleet was defeated by the Japanese. That was particularly humiliating because 60 or so years earlier, Japan was defeated by a single American gunboat - which was one of the factor that precipitated the so-called Meji restoration (rapid industrialization based mainly on German and French models) which transformed Japan into a world-class power. The defeat sparked wide protests which were brutally supressed by the authorities which managed to cling to power. The final blow came during the WW I as the Russian army under th eindept leadership was decimated by th eGermans. That weakened the regime to the point that revolutiuon was possible in February 1917 - but that still was not a socialist revolution, but a revolution of industrialists and reformers represented by the Kerensky government. The Kerensky government would have had survived, had not it made a grave mistake - it countinued the very unpopulr in Russia war effort against Germany on the request of its allies England and France (who feared that cease fire with Russia would free German forces to fight on the Western front). That decision created fertile ground for dissent - which was skillfully exploited by Bolsheviks & Co.
China followed a somewhat similar trajectory - the corrupt feudal empire was unable to transform itself (like Japan did under Meji) until 1920s - when the nationalist Sun Yatsen attempted a radical reform (btw, Sun Yatsen was the only nationalist leader worshiped under Mao) - but the modernization was stopped by the Japanese invasion. The exceptional brutality (even by fascist standards) of that invasion, in turn , radicalized the essentially conservative peasantry, which was skillfully captured by Mao in his move against the nationalists.
The bottom line is that Russia and China collapsed not because of capitalism but because of the lack of it. More specifically, the backward quasi-feudal regimes were literally destroyed by foreign powers (Germany and Japan) - which created an opportunity for a revolution. But even these revlotion were no initially a communist ones, but bourgeois revolutions aimed at modernization. The "communist" revolutions shortly followed these initial "bourgeois" revolutions as a result of radicalization of peasantry. In that respect, the Russian and Chinese revolution have more in commonwith Khmer Rouge and and the Taliban - namely they are all essentially peasant rebellions against ancien regime weakened by foreign powers - than with a trabsformation of a capitalist society to a socialist one, as envisioned by Karl Marx.
In fact, there has been not a single communit revolution in an industrial democracy - all such revolutions took place in backward, rural societies which further underscore their essentially peasant character. The only "revolutionary" force that managed to subvert an industrial democracy is fascism. With that track record, praying for a revolutionary overthrow of a capitalist society is a scary thing, indeed.
Wojtek