Seriously dude, do you even read the comments you reply to. Answering the same question again and again is really of putting. I'll answer this for the very last time in as comprehensive a way as possible, maybe you'll get it this time
The following factors are the determining factors to how developed a country is. Its not limited to them only though but they're the key determinants. They're health, Education and economy.
Health
-Life expectancy is 62yrs in Tz compared to 64yrs in Kenya.
-Doctor to patient ratio is 1:21000 in Tz vs 1:17000 in Ke.
-Infant mortality rate is 43.1/1000in Tz vs 38.3/1000 in Ke.
-Access to improved drinking water is 55.6%in Tz vs 63.2% in Ke
-Access to improved sanitation is 15.6% in Tz vs 30.1% in Ke
-HIV prevalence is 4.96% for Tz vs 5.91% in Ke.
-Hospital bed density per 1000 is 0.7beds/1000in Tz vs 1.4beds/1000in Ke
-Health expenditure as a % of GDP is 5.6% in tz vs 5.7% in Ke.
All according to UNICEF.
So in health, Ke is better in all but one metric
Education
-Literacy rate is 70%in Tz vs 78% in Ke.
-School life expectancy is 8yrs in Tz vs 11yrs in Ke.
-Education expenditure as a % of GDP is 3.5% in Tz vs 5.3% in Ke.
-College and university enrollment 0.7%for Tz, 3% for Ke
-No of universities is 41 in Tz vs 49 in Ke (only chartered universities)
-No of secondary schls 4291 in Tz vs 7308 in Ke
Number of secondary schools by Region - Total Number of Secondary School by region,2014 - Open Data Tanzania
Pealing the Mask; Facts on Secondary Education Sector in Kenya)
in education, Kenya leads in all metrics
economy and infrastructure
-GDP of $51bn in Tz vs $75bn in Ke
-GDP PPP is $163.5bn in Tz vs $164.3 in Ke
-HDI is 0.531 (Low human devt) in Tz vs 0.555 (lower Medium human devt) in Ke
-length of paved roads 7092km in Tz vs 14420km in Ke (2014)
- length of rail is 4567km in Tz vs 3806km in Ke.
-unemployment rate 33%in Tz vs 40% in Ke
-population below poverty line of $2 dollars 53%in tz vs 48% in Ke
-electricity production- 6.1bn KWH in Tz vs 9.2bnKWH in Ke
-electrification rate is 34%in Tz vs 65% in Ke
-pipeline length 899km in Tz vs 932km in Ke
-No of airports 166 in Tz vs 197 in Ke
-No of intnl airports with more than 2438km of paved runways 4 in Tz vs 7 in Ke
The World Factbook — Central Intelligence Agency
Kenya vs. Tanzania - Country Comparison
Kenya leads in all but 2 metrics
You made me make a very long post, go through it and you'll understand the developmental gap between Kenya and Tanzania. Kindly do not ask that question again if you can't get it after going through the above data.