Cash is printed by the government. There is almost no limit whenever government needs more cash they just print it which affects the whole country, but on the other hand Bitcoin is fixed there are only 21 million Bitcoins in the network which we can use. Cash can be stored in the Bitcoin is secured. Bitcoin is also instant but it takes time to collect witnesses which we call confirmation.
Cash is indeed an unlimited supply, the government can just print as many as they want, if needed. But as for those who have studied Economics very thoroughly, it does not work as easy as that. You see, as the quantity limits as the value increases. Therefore, if the government would print out, let's say a Billion Dollars, it would gradually affect the current overall net price of Dollars.
As well as the Bitcoin, you said that there are only 21 million Bitcoins available in the network, but how come that its price is still continuing on increase. Does that mean that the number of available Bitcoins are dwindling?