well 2 main reasons as i see it..
JDM regualtions. . which govern everythin from power outputs to external dimensions of the cars...
like for example Kei-Cars. the smallest of em all . .. like Suzuki Kei / Wagon-R / MR Wagon/ Honda Life / Diahatsu Mira... u can see they are all the same size . .leghth n width n engine sizes... cause the jap regualtions for kei-cars .. they are bound to be of so n so width n length . .n if they go beyond tht . .they are bagged wid heavy taxes. . this is a way of reducing congestion .. . the only place they are not governed is the height...
so these manufacturers push the limits of utilizing the given space to the maxx .. but given the small size . .the results can be claustrophobic.. so in order to give the cabin a light n open feel . .they maxximize the glasshouse !
anthropometrics !
see for urselves.. try sittin on a chair in an easy position .. like u do in a 89 honda civic. . ur legs stretch far forward .. so tht means u need more space in the cabin
but try sittin on a stool .. ok not a wooden one .. but a bar stool ... a bit higher than the chair but not too upright. . the same seating as in the new city or altis corolla... u sit a bit upright . n ur legs dont stretch as far forward .. so which means .. . the same cabin space which was fallin short of leg room has now become ok! cause ure sittin a bit higher n just as comfortable.....
i guess most of u will see the light .. n if u dont . .forgive me .. its jst an industrial designer's perspective of lookin at things. ..
there might b more thn jst these reasons. but they do count !