By the third century much of imperial society was in permanent crisis: wracked by famine, devastated by the consequences of continuous wars and political upheaval, crippled by the burden of taxation, and afflicted with severe economic dislocation. The Roman Theatre and Its Audience, p. 192
Reined in tightly to the imperial economy through their dependence on stipends, with only a fraction of the landholdings they had enjoyed under the Ptolemies, the temples of Egypt were doomed to follow the empire's spiral downward spiral in the various economic catastrophes of the third century. Where the munificence of Augustus and the first-century emperors appears in temples throughout Egypt, the effects of the third century crisis on the temple infrastructure are rather stark: a drastic decline in building dedications and other inscriptions. Temples, at least the major ones, seem to be in a state of progressive ruin, dwindling vestiges... Religion in Roman Egypt: Assimilation and Resistance, p. 27.
Striking deep into Syria, [Shapur] sacked and plundered many wealthy cities in his path, including the great city of Antioch on the Orontes. Renewing the offensive in 253, his progress was only halted by the hereditary priest-lord, Uranius Antoninus. Aurelian and the Third Century, p. 28
This was poetic justice for legio III Cyrenaica, whose temple at Bostra the Palmyrenes had destroyed when they overran Arabia... The great Bel Temple in Palmyra was not destroyed, though it may have been pillaged.
Empress Zenobia: Palmyra's Rebel Queen, p. 154
Should I also bring the accounts of Jordanes about the conquests and devastation incurred by the Huns, or Tabari about the conquest of the majority of the West Asian and African portions of the Roman Empire by the Arab Muslims? I only focused on the third century after all. With all these wars, conquests and economic crises, it isn't hard to see why the traditional Greco-Roman religion with all its expensiveness didn't survive and got replaced by Christianity.