I agree with @abdulrehmanrauf about you being unlucky.
There can be many reasons for this, quality of lubricant oil seems to be the most important one. The other thing is the air quality in Lahore. When I was in Lahore I used old Havoline Formula 3, (no longer available) an excellent quality lubricant and changed it after 800 km, but I cleaned the air-filter after 300-350 km. But Sprinter has a better air-filter so changing around 1,000 km should be OK if the oil is authentic and you clean the air filter at least once around 500 km. I haven't used Sprinter since early 2008 so I don't remember if the air filter requires 2-stroke oil, if it does then you have to be careful to use just the right amount and that it is distributed evenly.
Company recommendations have to be in accordance with international recommendations, you may have to change it for your conditions, for Lahore I would say change the oil-filter every 2,000 km or every other oil-change. I live in Abbottabad, air is much cleaner but I change the oil-filter every 2,000 or 3,000 km(on my GS150), depending on the colour of the removed lubricant.
If you use Shell I would recommend that you buy it from company owned fuel stations, the main Shell station at Liberty Market used to be company owned.
I use Zic 4T (or is it T4?) bought from Zic Distributer in Abbottabad and use it for at least 1,000km. While I was on a visit, I bought it from a shop in Lahore and used it and had to replace if after 500 km when I came back to Abbottabad and found that the bike had problem on climbs, had no power and I had to use first or second gear on climbs that otherwise mostly used third gear and second if I had to slow down because of traffic. On flat roads it is not that clear so you have to make sure that you are buying authentic lubricant.