Well anna to be honest we know why for certain key events like IPL or BCCI cricket broadcasters or OTT platforms r wanting to use every free second available to stream ads and earn revenue bcoz they have invested a huge amount in buying rights...also other sporting properties for which they acquire rights too come at very high price but generate not that much revenue hence to accommodate all these things they look out for ways to maximise revenue be it thru ads or via providing sports channels or OTT subscription in bundled packages.
Coming to ur 2nd point, OTT itself has a very small subscriber base compared compared to Pay TV universe and within this small base there would hardly 1% willing to buy premium ad free subscription costing a lot ....still the larger public who r coming onto OTT platforms look for affordable way to watch content and are fine with ads. OTT platforms have hence developed / are developing various business models to enlarge their subscribe base & maximise revenue....there freemium model where certain mass content is made available for free & revenue is earned thru ads then there r somewhat affordable mobile and other plans which provide choice to people to opt for a plan which suits their budget and these have ads playing while content is streaming thus adding a balance between revenue earned thru subscription + ads. All these business models will co-exist so as to expand the OTT growth.
Remember not just sporting properties but in general rights of other content or cost involved in making original shows and even operational costs associated with running an OTT platform with host of services + features is extremely high thus lower priced subscription plans cannot help the platform recover huge investments and earn profit. Even if we r saying say Rs. 100 or 150 per month for regular OTT plans or Rs. 50 or 60/month for mobile only plans of a broadcaster then we r getting content spanning so many genres....If u combine the price of channels of that broadcaster u pay for month on DTH / Cable Platform to what we pay to same broadcaster via its OTT platforms then OTT still costs very less and is quite affordable for the large variety of content we get to watch on it....u can even have a broader comparison by combining monthly channel costs we pay for all key channels of leading broadcasters vs what we pay for their OTT Platforms and still OTT is very affordable. Just like TV Channels despite having much larger viewer base require ad revenue to remain financially viable then OTT with a lot smaller audience base also does require ad revenue to cater to general audience via affordable OTT subscription plans...even if hypothetically around 20 or 30 years from now OTT subscriber base reaches to current TV universe level still ads would remain to be part of their revenue model.
Coming to initial ad free experience claims made by OTT platforms those r similar to what HD channels used to say when they were launched as in intial phase companies try to attract maximum people and initially brands do not buy ad slots on channels particularly for premium category ones hence in this window such strategies r worked out by companies / broadcasters to build buzz about the channels / OTT platforms...later Ad Free option remains but such plans cost very high as is the case now on OT while for TV same is not possible