You must be thinking where will OLA and Uber keep their black money. So actually uber and OLA does not themself generate black money but instead they lead to the transactions which does not have any records and thus Indian Government does not get any taxes on those transactions.
HOW?
This happens when you pay in cash and the driver does not have change to return you back. You considering the change as a small amount gives to driver thinking how it will harm you. This change is the transaction which is not getting recorded and thus Indian Government losses tax on it.
Very rough Estimation for demo purpose
Lets talk about UBER, they have around 250,000 drivers present on their platform.
Lets say they generate minimum of 20 rupees on an average thus leading to 250000 * 20 = 5000000 , which is 50 lakhs per day. Now for an year total is 5000000 * 365 = 1825000000. Which is one hundred and eighty two crore. This much is the amount that is not recorded. Now on this money Uber drivers has to pay taxes. generally uber drivers wage is from 40 K and above.
Keeping this in mind the total earning will be more than 5 lakhs thus taking him in slab of 20% income tax. Now Indian government in losing 20% of 1825000000 which is 0.2 *1825000000 = 365000000. The amount is thirty six crore and fifty lakh. Thus Indian government is losing this much amount of money.
Here I have taken very rough estimation of how much black money is generated with very minimum values. This can be wrong sotry doing the maths yourself.
Also not only this anywhere you are using cash to pay where the prices are like 199 or 1999 or anything like this. You forgot to get the 1 rupees back, which is adding to the loss of Indian Government. This one rupee when accumulated from huge number of stores and sells lead to a huge amount which is in hundreds of crores.
Suggestion
So if you against the black money and want the government to get all the taxes so they can spend on you avoid using cash.
Go cashless and always ask for receipt else you have contributed in black money generation.
Also read about :
https://life.learnsteps.com/much-scrapping-currency-india-fair-questions-unaswered/
https://www.learnsteps.com/what-if-you-burn-your-1000-rs-note/